Pressures in Archaeal Protein Coding Genes: A Comparative Study

Our studies on the bases of codons from 11 completely sequenced archaeal genomes show that, as we move from GC-rich to AT-rich protein-coding gene-containing species, the differences between G and C and between A and T, the purine load (AG content), and also the overall persistence (i.e. the tendency of a base to be followed by the same base) within codons, all increase almost simultaneously, although the extent of increase is different over the three positions within codons. These findings suggest that the deviations from the second parity rule (through the increasing differences between complementary base contents) and the increasing purine load hinder the chance of formation of the intra-strand Watson–Crick base-paired secondary structures in mRNAs (synonymous with the protein-coding genes we dealt with), thereby increasing the translational efficiency. We hypothesize that the ATrich protein-coding gene-containing archaeal species might have better translational efficiency than their GC-rich counterparts

Mutantes resistentes à Antibióticos em Xanthomonas Campestris (Fammel) Dowson

O presente trabalho, visou o estudo de mutantes resistentes à antibióticos na bactéria fitopatogênica Xanthomonas campestris (Pammel) Dowson. Foram obtidos mutantes resistentes à cinco antibióticos: penicilina, estreptomicina, aureomicina, cloranfenicol e éritromicina. O incremento de resistência em relação à linhagem original foi 4 vêzes para a penicilina, 8 para o cloranfenicol, 32 para a aureomicina e pelo menos 16 e 128 vêzes para a éritromicina e estreptomicina respectivamente. Em nenhum dos casos, verificou-se resistência cruzada ou sensibilidade colateral.The present paper deals with study of mutants resistants against five antibiotics in a phytopathogenic bacterium Xanthomonas campestris (Pammel) Dowson. One-step mutants to streptomycin and erythromycin were isolated. For the penicillin, aureomycin and chloranphenicol multiple-step mutants appeared the sensitive populations were grown in gradient plates with antibiotics. The resistance increase was 4 fold for the penicillin, 8 fold for the chloranphenicol, 32 fold for the aureomycin; 16 fold for the erythromycin and 128 fold for the streptomycin. It was not found cross resistance or collateral sensitivity when a certain antibiotic was tested against the others drugs