RESUMO
The HU protein isolated from Escherichia coli, composed of two partially homologous subunits, alpha and beta, shares some of the properties of eucaryotic histones and is a major constituent of the bacterial nucleoid. We report here the construction of double mutants totally lacking both subunits of HU protein. These mutants exhibited poor growth and a perturbation of cell division, resulting in the formation of anucleate cells. In the absence of HU, phage Mu was unable to grow, to lysogenize, or to carry out transposition.
Assuntos
Proteínas de Bactérias/deficiência , Proteínas de Ligação a DNA/deficiência , Escherichia coli/genética , Mutação , Proteínas de Bactérias/genética , Bacteriófago mu/genética , Bacteriófago mu/crescimento & desenvolvimento , Clonagem Molecular , Elementos de DNA Transponíveis , Proteínas de Ligação a DNA/genética , Escherichia coli/crescimento & desenvolvimento , Genes Bacterianos , Lisogenia , Plasmídeos , Transcrição GênicaRESUMO
Germinating spores of Bacillus subtilis mutants which lack small, acid-soluble spore proteins alpha and beta did not exhibit the transient elevated UV resistance seen during germination of wild-type spores.
Assuntos
Bacillus subtilis/efeitos da radiação , Proteínas de Bactérias/deficiência , Fator sigma , Fatores de Transcrição , Raios Ultravioleta , Bacillus subtilis/genética , Dano ao DNA , DNA Bacteriano/efeitos da radiação , Esporos Bacterianos , Fatores de TempoRESUMO
Loss of small, acid-soluble spore protein alpha reduced spore UV resistance 30- to 50-fold in Bacillus subtilis strains deficient in pyrimidine dimer repair, but gave only a 5- to 8-fold reduction in UV resistance in repair-proficient strains. However, both repair-proficient and -deficient spores lacking this protein had identical heat and gamma-radiation resistance.
Assuntos
Bacillus subtilis/efeitos da radiação , Proteínas de Bactérias/deficiência , Reparo do DNA/efeitos da radiação , Dímeros de Pirimidina/deficiência , Fator sigma , Fatores de Transcrição , Raios Ultravioleta , Bacillus subtilis/metabolismo , Bacillus subtilis/fisiologia , Esporos Bacterianos/efeitos da radiaçãoRESUMO
Previous DNA sequence analysis of bleomycin-induced forward mutations in repackaged lambda phage has suggested SOS-dependent replicative bypass of oxidized apyrimidinic sites as a possible mechanism of mutagenesis. In order to evaluate this hypothesis further, frequencies of mutation to a clear-plaque phenotype were compared for bleomycin-damaged phage grown in various repair-deficient strains of Escherichia coli. Survival of bleomycin-damaged phage was virtually identical in all host strains. Studies in SOS-deficient strains indicated specific requirements for functional recA+ and umuC+ alleles in the generation of the majority of bleomycin-induced mutations, as well as a less stringent requirement for induction of the SOS response by ultraviolet irradiation of the host cells. These results are expected for mutagenesis resulting from apyrimidinic sites. However, the mutation frequency for bleomycin-damaged phage was the same whether the phage were grown in a wild-type strain or in strains deficient in apurinic/apyrimidinic repair endonucleases; this was true even for an nth-nfo-xth- strain lacking all three major apurinic/apyrimidinic endonucleases (endonuclease III, endonuclease IV, and exonuclease III). Likewise, phage grown in an endonuclease IV-overproducing strain showed the same mutation frequency as those grown in wild-type cells. These data suggest that either i) bleomycin-induced mutagenesis results from SOS-dependent bypass of lesions other than apyrimidinic sites or ii) the number of apyrimidinic sites available for SOS processing is virtually independent of the level of apurinic/apyrimidinic endonuclease activity in the cell. It is possible that a fraction of the apyrimidinic sites induced by bleomycin either are intrinsically resistant to repair or undergo secondary reactions that render them resistant.
Assuntos
Bacteriófago lambda/efeitos dos fármacos , Bleomicina/farmacologia , Reparo do DNA , DNA Viral/efeitos dos fármacos , Proteínas de Escherichia coli , Escherichia coli/fisiologia , Resposta SOS em Genética , Proteínas de Bactérias/deficiência , Bacteriófago lambda/genética , DNA Viral/genética , DNA Liase (Sítios Apurínicos ou Apirimidínicos) , Desoxirribonuclease (Dímero de Pirimidina) , Desoxirribonuclease IV (Fago T4-Induzido) , Endodesoxirribonucleases/deficiência , Escherichia coli/enzimologia , Exodesoxirribonuclease V , Exodesoxirribonucleases/deficiência , MutaçãoRESUMO
Using a variety of immunological techniques, the supernatant levels of ribosomal proteins were measured in mutants lacking the ribosomal proteins L1 or L11, and in wild-type strains. There was a 2.5--5-fold elevation of protein L11 level in the supernatant of strains lacking protein L1, compared to wild-type. In contrast, there was no elevation, but rather a diminution, in the corresponding L1 level in strains lacking protein L11, compared to wild-type. These results are consistent with a model for the control of expression of the L11-L1 operon in which protein L1 is an inhibitor of expression of that operon, but protein L11 is not. The supernatant concentrations of other proteins were indistinguishable in all strains.
