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The pattern of protein synthesis changes soon after fertilization of clam oocytes. The most abundant of the mRNAs whose translation increases at this time encode ribonucleotide reductase and the A- and B-type cyclins. These mRNAs have been cloned and sequenced, yet their sequences do not show regions of similarity that could explain the masking mechanism. However, these mRNAs retain their 'masked' state in cell-free translation assays and their translation can be activated by gel filtration in high salt, which probably removes repressor proteins. A 'competitive unmasking' assay was used to identify the protein-binding regions of each mRNA. This involved adding short segments of antisense RNA that annealed to the mRNA and displaced the repressors. The unmasking regions in ribonucleotide reductase and cyclin A mRNAs revealed by this assay are 120-140 nt long and are located in the central portions of the 3' non-coding regions.

Urinary excretion of alanine aminopeptidase, alkaline phosphatase, gamma-glutamyltransferase and N-acetyl-beta-D-glucosaminidase was determined in gel-filtered samples of morning random urine specimens of 442 subjects of various ages (5 days to 58 years). Enzyme excretion related to urinary creatinine (enzyme/creatinine ratio; U/mmol creatinine) significantly decreased with increasing age. Sex-related differences of some enzyme excretions were found in age groups over 6 years. From these investigations, we calculated upper reference intervals (97.5 percentiles) for 5 age-dependent groups of children and adolescents and for one group of adults.

The following reviews the role of mRNA stability in the regulation of both viral and cellular gene expression in virus-infected cells. Indeed, several eukaryotic viruses, including the human immunodeficiency virus, HIV-1, regulate cellular protein synthesis via such control mechanisms. The following systems will be discussed: (i) the degradation of viral and cellular mRNAs in cells infected by herpes simplex virus (HSV) and advances made using the HSV virion host shutoff mutant; (ii) the degradation of viral and cellular mRNA and ribosomal RNA in cells infected by vaccinia virus and the possible role of the oligoadenylate synthetase-RNase L pathways; (iii) the turnover of RNAs in cells infected by encephalomyocarditis virus, reovirus, and La Crosse virus; and finally (iv) recent studies from our laboratory on the degradation of cellular mRNAs in cells infected by HIV-1.

A discrete deficiency of hepatic ornithine transcarbamylase (OTC) was found in male patients who were 58, 46 and 17 years old. Each had developed hyperammonemic coma. The mother and a sister of the 17-year-old patient exhibited orotic aciduria either spontaneously or after protein loading, thus demonstrating heterozygosity. A sister of one other patient and a daughter of the third patient showed a smaller orotic aciduria after protein loading. These observations indicate that inherited deficiency of OTC should be included in the differential diagnosis of hyperammonemic states in adult male patients.

The lysosomal storage disease beta-mannosidosis, described in both goats and humans, can be detected by measuring a deficiency in hydrolysis of the fluorogenic substrate 4-methylumbelliferyl-beta-D-mannoside. An inhibitor of guinea pig beta-mannosidase (beta-man) activity was detected when tissue was homogenized in phosphate-buffered-saline (pH 7.4) containing 0.25 mol/l sucrose. The existence of such an inhibitor was apparent when the enzyme was immunoprecipitated from tissue using a specific beta-man polyclonal antibody. There was up to a threefold increase in activity in the immunoprecipitated enzyme (antibody-enzyme complex) compared to the activity of the nonimmunoprecipitated enzyme. An extensive study was therefore undertaken to determine the nature and specificity of this inhibitor by analyzing the effect of a range of metal ions and sugars on beta-man activity compared to other lysosomal hydrolase activities. Although ferrous, ferric, cobalt, and manganese ions were highly inhibitory to beta-man, they also inhibited other lysosomal hydrolases to a similar extent. Likewise, mannose inhibited both alpha- and beta-man activities equally. The only compound to specifically inhibit beta-man in a manner similar to that observed in the tissue homogenate was glucosyl(beta, 2)fructofuranoside (sucrose). This is an important finding in that tissue samples are commonly prepared in buffers containing sucrose and this could lead to a wrong diagnosis of beta-man deficiency. In order to determine if the absence of an activator factor or alternatively the presence of a specific inhibitor was a contributing factor in the lack of beta-man activity in cultured fibroblasts from affected humans and goats, mixing studies with normal and affected cell extracts were performed but no restoration or inhibition of beta-man activity was found.

The mRNAs coding for ribosomal proteins (rp-mRNA) are subjected to translational control during Xenopus oogenesis and embryogenesis, and also during nutritional changes in Xenopus cultured cells. This regulation, which appears to respond to the cellular need for new ribosomes, operates by changing the fraction of rp-mRNA engaged on polysomes, each translated rp-mRNA molecule always remaining fully loaded with ribosomes. All rp-mRNAs analyzed up to now show this translational behavior, and also share some structural features in their untranslated portions. In particular they all have rather short 5' untranslated regions, similar to each other, and always start at the very 5' end with a stretch of several pyrimidines. Fusion to a reporter-coding sequence of the 5' untranslated region of r-protein S19 has shown that this is involved in the translational regulation.

Rapid turnover of the c-myc message mediates both the low basal level of mRNA and the rapid response to changes in transcription. The primary RNA instability determinant (RID sequence) resides in the 3' untranslated region (UTR), within an 80 base region that is rich in A and U residues. In contrast to granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA in which the RID sequence has been mapped to a repeating AUUUA sequence, mutation of the only copy of this sequence in the c-myc 3' UTR has no effect on RNA turnover. Thus the c-myc RID sequence appears to be quite different from that of GM-CSF, which may account for the differential regulation of half-life exhibited by these mRNAs. c-myc mRNA turnover is also tightly coupled to translation since translational inhibitors stabilize this mRNA. Mutation of the initiating AUG to a termination codon stabilizes c-myc RNA, arguing that loading with polysomes (perhaps accompanied by localization on the cytoskeleton) is also required for proper message turnover.

Influenza virus type A has been shown to establish a translational control system such that during infection there is a dramatic inhibition of host cell protein synthesis and viral mRNAs are selectively and efficiently translated. The following review summarizes the complex strategies employed by influenza to accomplish these goals. These include: (i) preventing newly made cellular mRNAs from entering the cytoplasm of infected cells; (ii) inhibiting the initiation and elongation steps of translation of preexisting cellular mRNAs; (iii) possessing RNAs with structural features which enhance translation; (iv) encoding mechanisms to downregulate the interferon induced protein kinase thus allowing overall protein synthesis levels to remain high.

Serum beta-N-acetylhexosaminidase levels in 49 patients with inflammatory bowel disease (IBD; 23 patients with ulcerative colitis, 10 with Crohn's disease, and 16 with ileostomy after total proctocolectomy) as well as in healthy normal controls were determined. They were found to be significantly elevated in 91% of all patients, disregarding the state of activity of the disease. It seems most likely that activated macrophages are the source of this lysosomal hydrolase in the serum of IBD patients since other theoretical possibilities, like damaged hepatocytes or elevated serum bile acid levels, are not relevant for these patients.

Picornaviruses are mammalian plus-strand RNA viruses whose genomes serve as mRNA. A study of the structure and function of these viral mRNAs has revealed differences among them in events leading to the initiation of protein synthesis. A large segment of the 5' nontranslated region, approximately 400 nucleotides in length, promotes 'internal' entry of ribosomes independent of the non-capped 5' end of the mRNA. This segment, which we have called the internal ribosome entry site (IRES), maps approximately 200 nt down-stream from the 5' end and is highly structured. IRES elements of different picornaviruses, although functionally similar in vitro and in vivo, are not identical in sequence or structure. However, IRES elements of the genera entero- and rhinoviruses, on the one hand, and cardio- and aphthoviruses, on the other hand, reveal similarities corresponding to phylogenetic kinship. All IRES elements contain a conserved Yn-Xm-AUG unit (Y, pyrimidine; X, nucleotide) which appears essential for IRES function. The IRES elements of cardio-, entero- and aphthoviruses bind a cellular protein, p57. In the case of cardioviruses, the interaction between a specific stem-loop of the IREs is essential for translation in vitro. The IRES elements of entero- and cardioviruses also bind the cellular protein, p52, but the significance of this interaction remains to be shown. The function of p57 or p52 in cellular metabolism is unknown. Since picornaviral IRES elements function in vivo in the absence of any viral gene products, we speculate that IRES-like elements may also occur in specific cellular mRNAs releasing them from cap-dependent translation. IRES elements are useful tools in the construction of high yield expression vectors, or for tagging cellular genetic elements.