Extrachromosomal elements as possible agents of adaptation and development.

Abstract

INTRODUCTION............................................................. 552 MOLECULAR MECHANISMS OF EVOLUTION ....... ........................ 553 INSUFFICIENCY OF THE CLASSICAL MECHANISM(S) ...... ................ 553 Two Types of Molecular Evolution ............................................ 553 Role of Mutation ............................................................ 554 MUTATION: A REEXAMINATION ........... ................................. 555 STREPTOMYCIN RESISTANCE: A COMPARISON OF TWO ADAPTIVE MODES 556 TERMINOLOGY OF ECEs ................ .................................... 557 ECOLOGY OF ECEs......................................................... 558 HOST RANGES OF ECEs IN NATURAL ECOSYSTEMS ...... ................. 560 GENES CARRIED BY ECEs .............. .................................... 561 GENETIC "COMPLEXITY" OF A PROKARYOTIC SPECIES ...... ............ 563 GENETIC PROCESSES MEDIATED BY ECEs ....... ......................... 567 Dissemination of Existing Genes ........... .................................. 567 cell-to-ECE-to-cell gene transfer ............................................ 567 phage conversion........................................................... 567 ECE-to-cell-to-ECE gene transfer .......... ................................ 568 Genome Sizing ............................................................... 568 Controlled Randomization of Genomes ........................................ 568 IS elements and phage Mu ............. .................................... 568 permuted phage genomes ................................................... 569 Natural Genetic Engineering ............. .................................... 569 processes of polynucleotide exchange involving resident homology ..... ....... 569 polynucleotide exchange involving nonresident homology ...... .............. 571 evolution of R factors in bacteria .......... .............. ..................... 572 significance of sequence duplication in natural genetic engineering ..... ...... 572 universality and frequency of natural genetic engineering ...... .............. 574 Miscellaneous......................................... ..................... 575 OTHER EVIDENCE FOR POSSIBLE PROCESSES OF ECE-MEDIATED POLYNUCLEOTIDE EXCHANGE ........... ................................. 575 Dispersed State of Specific (Plant) Proteins ........ ........................... 575 "Simultaneous" Appearance of Similar Genes in Unrelated Organisms ..... ..... 575 PROCESSES OF POLYNUCLEOTIDE EXCHANGE AMONG EUKARYOTES ... 576 POSSIBLE INVOLVEMENT OF ECEs (RNA TUMOR VIRUSES) IN EMBRYOGENESIS ............................................................... 576 RNA TUMOR VIRUSES IN INTERSPECIFIC GENE TRANSFER ..... ......... 577 RNA TUMOR VIRUSES AND REGULATORY PROCESSES IN HIGHER ORGANISMS ................................................................. 578 EPIGENETIC ELEMENTS IN ANIMALS AND IN PLANTS ...... .............. 578 POSSIBLE CANDIDATES FOR EPIGENETIC AGENTS IN PLANTS ..... ...... 579 Viroids...................................................................... 579 Control Elements ............................................................. 579 Geometrical Plant Viruses .......... ......................................... 579 AN INTEGRATED THEORY OF EVOLUTION ................................ 580 LITERATURE CITED...................................... 582