Journal of molecular and applied genetics最新文献

Napins are a family of small, basic storage proteins synthesized in Brassica napus (rapeseed) embryos during seed maturation. Cultured embryos also synthesize napins but require exogenous abscisic acid (ABA) to maintain high accumulation rates. We synthesized cDNA from total RNA of embryos cultured on a medium containing ABA, and cloned it into the Pst1 site of pBR322. Two clones containing napin cDNA sequences selected by differential colony hybridization using [32P]cDNA probes from embryos grown with or without ABA were analyzed. These clones, pN1 (insert size = 583 bp) and pN2 (insert size = 739 bp), contained cDNA from two different napin mRNAs. The mRNAs to which they hybridized were found to encode a 21,000-dalton polypeptide that was immunoprecipitated by antibodies to mature napin (subunits of 9,000 and 4,000 daltons). The cDNA clones hybridized to an 850-base mRNA. Nucleotide sequencing demonstrated 95% homology between pN1 and pN2 cDNA inserts and predicted a precursor polypeptide of 178 amino acids, consistent with the 21,000 dalton in vitro translation product. Comparison of the deduced amino acid sequence with published amino acid compositions of mature napin subunits suggests that both the large and the small subunits are present in one precursor polypeptide, and that other regions of the precursor are removed during processing.

The FT37/1 tumor line induced by Agrobacterium tumefaciens on flax epicotyls contains 22-24 copies of the T-DNA encoded nopaline synthase gene per cell. All the gene copies are methylated to some extent but the methylation is not uniform, nor does it reflect the methylation level of the flanking plant DNA. This extensive methylation correlates with an extremely low level of expression of the nopaline synthase gene. Treatment of the tumor line with the in vivo demethylating drug 5-azacytidine at a concentration of 3 X 10(-5) M, resulted in the demethylation of, on average, one copy of the nopaline synthase gene per cell. This demethylation was paralleled by an increase in the transcription of the gene and indicates that cytosine methylation is capable of suppressing the expression of plant genes in vivo.

Transfection of monkey cells with recombinant plasmids containing a beta-globin coding region fused to wild-type or deleted simian virus 40 (SV40) early region promoters has allowed an analysis of the transcriptional activity of these promoters in the absence of repression by large T antigen. We find that deletion of the TATA sequence does not reduce the transcriptional effectiveness of the promoter; however, the 5' ends of the transcripts are heterogeneous rather than being restricted to the usual sites. The short GC-rich repeat sequences between nucleotides 37 and 107 and the tandemly repeated 72-bp segment between nucleotides 107 and 250 are each essential for promoter function. The GC-rich repeats are functionally redundant and probably interchangeable, since several subsets of two or three of the GC-rich segments are sufficient. One copy of the 72-bp sequence is sufficient to permit transcription. Moreover, the 72-bp repeat sequences function normally even if they are inverted relative to their normal orientation.

The structure and expression of the Shrunken (Sh) locus have been examined in several maize strains with mutations at the locus caused by the controlling element Dissociation (Ds). Three of the strains (sh-m6233, sh-m5933, and sh-m6258) are of independent origin, and the fourth (sh-m6795) represents a spontaneous recessive sh allele derived from an Sh revertant of strain sh-m6258. The sh-m6233 and sh-m5933 strains produce undetectable levels of the Sh-encoded sucrose synthetase and very small amounts (less than 1%) of an apparently normal sucrose synthetase mRNA in immature endosperm tissue. Both strains have rearrangements affecting the structure of the locus near the 5' end of the transcription unit. The Sh locus in the related strains sh-m6258 and sh-m6795 is interrupted by an insertion or a rearrangement having one breakpoint in an intervening sequence near the 3' end of the mRNA coding sequence. The 5' end of the gene is transcribed in immature kernels of both mutants, giving aberrant poly (A)+ mRNAs that are homologous to the normal transcript up to the insertion or rearrangement breakpoint and lack homology to the 3' end of the gene. The aberrant transcripts from both strains are translated in vivo and in vitro, yielding 82- and 85-kD proteins that are immunologically related to the 92-kD Sh-encoded sucrose synthetase monomer.

Using specific mutants as a means of identification, the bacterial protein for asparagine synthetase (Asn Syn) was shown to be antigenically and electrophoretically similar to its mammalian counterpart. This observation prompted us to attempt direct transfer of the cloned bacterial gene for the enzyme to mammalian cells. DNA from the replicative form of clone M13 OriC, containing the bacterial gene for Asn Syn, was shown to be capable of causing transformation of Jensen rat Asn Syn- cells to cells capable of growth in Asn-free medium; no prior modification of the bacterial gene was required. This relatively inefficient transformation (20 colonies/micrograms DNA/10(6) cells) was sensitive or insensitive to restriction enzyme digestion of the M13 OriC DNA in complete agreement with the known restriction map of the bacterial gene. Clones of transformed rat cells contained the bacterial DNA, which was amplified if increased levels of the enzyme were demanded and lost if selection was removed. The clones also contained polysomal bacterial RNA and a new protein with properties similar but not identical to those of the bacterial enzyme. The biological significance of this unusual degree of compatibility between the prokaryotic and eukaryotic Asn Syn gene systems is discussed.

The trifunctional trp-1 gene from Neurospora crassa was cloned by complementation of a phosphoribosylanthranilate isomerase-deficient mutant of E. coli. A 2.7-kb DNA sequence containing trp-1 was determined. Homology of the deduced trp-1 polypeptide sequence to the corresponding E. coli proteins is striking; the order of functional domains within trp-1 is NH2-glutamine amidotransferase-indoleglycerolphosphate synthase-phosphoribosylanthranilate isomerase-COOH (NH2-trpG-trpC-trpF-COOH). Whereas trpF complementing activity can be detected in E. coli, trpC activity is absent. It is likely that translation of trp-1 does not proceed from the proper start site in E. coli; the carboxy terminal portion of the trp-1 polypeptide may be the only portion synthesized. Fusion of a bacterial amino terminus and ribosome binding site to the trp-1 coding region results in expression of trpC as well as trpF activity in E. coli. The locations of several startpoints for trp-1 mRNA synthesis were determined by the S1 nuclease mapping technique. DNA immediately 5' to the trp-1 transcription initiation region does not possess a sequence resembling the canonical TATAAA of eukaryotes.

A contiguous region of cellular DNA sequence, 64 kb in length and representing overlapping cellular inserts from three independent cosmid clones, has been isolated from a representative library of human lung carcinoma DNA partially digested with MboI. Within this region of the cellular genome, v-abl homologous sequences are dispersed over a total region of around 32 kb. These sequences represent the entire v-abl human cellular homologue, are colinear with the viral v-abl transforming gene, and contain a minimum of seven intervening sequences. At least eight regions of highly repetitive DNA sequences have been shown to map in close proximity to c-abl coding sequences. In addition to the major c-abl human locus, three regions of human DNA sequence, corresponding to only portions of the v-abl gene, have been identified. Two of these have been molecularly cloned and shown to be distinct from the primary human c-abl locus. Upon transfection to rat embryo fibroblasts in culture, none of the cosmid DNAs containing v-abl homologous sequences exhibited transforming activity. These findings identify and map a single genetic locus of human DNA, c-abl, representing the complete v-abl homologue, and demonstrate the existence of additional human DNA sequences corresponding to more limited, subgenomic regions of v-abl.

The purpose of this study was to evaluate the usefulness of randomly isolated human cDNA clones as probes for human restriction fragment polymorphisms. Clones were chosen from two human cDNA libraries and tested by hybridization against Southern blots of genomic DNA prepared from nine individuals. Three types of hybridization patterns were seen with the individual clones tested, those representative of single copy genes, others representative of gene families, and one characteristic of a mitochondrial gene. Only two of these cDNA clones revealed any polymorphisms among the individuals tested: pDK-08 and RW12, both representative of gene families. Both revealed independent polymorphisms with several of the restriction enzymes tested, and inheritance of these polymorphisms as Mendelian alleles was verified by human pedigree analysis. The results are discussed with regard to the usefulness of such cDNA clones in revealing polymorphisms in human genetic analysis.

Gene fusions between the Escherichia coli lacZ gene and DNA segments containing the simian virus 40 early promoter or the mouse mammary tumor virus (MMTV) promoter direct the synthesis of functional beta-galactosidase in Cos 7 monkey cells and mouse Ltk-cells. Enzymatic activity was measured either 72 h after transfection or in stable transformants. The sensitive beta-galactosidase assay was used to measure gene expression and to optimize the efficiency of DNA-mediated transfection. Glucocorticoids stimulated the production of beta-galactosidase when lacZ was fused to the hormonally regulated MMTV promoter.