Gene, 134 (1993) 15-24 15 GENE 07350 usage; gene expression; G + C content; mutation pressure; molecular evolution) Area of Microbiology, Department of Ecology, Genetics and Microbiology, Faculty of Biology, Universityof León, 24071León, Spain Received by K.F. ChaleT: 7 January 1993; Revised/Accepted: 19 April/22 Apri11993; Received at publishers: 17 June 1993 SUMMARY the amino acid (aa) residues of the BLCG \1 species, non-pathogenic, are used in the production of of the so-called glutamic acid-producing corynebacteria Brevibacterium sp., which are well defined on the basis of and Komagata, 1970). Two of the aa-producing coryne- codons; lb, kilobase(s) or 1000 bp;Nc, effective number of codons used