Merodiploid Ribosomal Loci Arising by Transformation and Mutation in Pneumococcus

Abstract

Merodiploid states have been detected in the ery and str loci of the pneumococcal genome. They are associated with particular mutations ( ery-r10 and str-d2 ) which add to, rather than replace their homologous sites during deoxyribonucleic acid (DNA)-mediated transformation. Markers at linked sites do not become diploid at the same time. The heterozygous condition thus produced is maintained during cell reproduction. However, in the case of the ery merodiploid at least, segregation of haploid types does occasionally occur. The transforming properties of DNA isolated from the merodiploids, taken together with the segregation patterns of the merodiploids, reveal the heterozygous condition. The merodiploid condition can be transferred via a single molecule of DNA, which can be explained by assuming that both alleles at the diploid site are integrated into the linear continuity of the bacterial chromosome. In the case of the ery merodiploid, two distinct, relatively stable but interconvertible states are recognizable. Their interconvertibility, as well as the segregation of hapliod descendants, can be explained as the result of occasional pairing of the duplicated regions with loss of one of these duplicated regions by recombination.

Mapping of Antibiotic Resistance Markers in Mycobacterium smegmatis

“…This was the reason why the frequency of met+nekr or met+vicr recombinant formation was particulary low ( Table 5). Such a stable heterogenote was also reported in recombinants of E. coli [6], in intergeneric recombinants between E. coli and S.typhimurium [11], and in transformants of Pneumococcus [13]. In pneumococci, the stable heterogenomic state was observed in the particular ribosomal genes, ery and str.…”

“…In pneumococci, the stable heterogenomic state was observed in the particular ribosomal genes, ery and str. The following hypotheses might be considered to explain the nature of such a stable heterogenote: a) nek and vic loci of strains R and P are both nonallelic and haploid recombinants possessing both resistant and sensitive alleles, b) nek and vic loci of R and P are allelic, but the loci of R are integrated into the recombinant chromosome by insertion without losing the allelic loci of P, as reported in Pneumococcus [13], c) recipient strain P has multiple copies of nek and vic, and in heterogenomic recombinants, one of these copies is replaced by the allele of R leaving the other(s) free, d) nek and vic of R are not integrated into the recombinant chromosome but exist as exogenotes.…”

Genetic Studies Relating to the Production of Transformed Clones Diploid in the Tryptophan Region of the Bacillus subtilis Genome

“…The features of this system studied so far can be summarized as follows. As in the cases of relatively stable merodiploids in pneumococcus (6,7,14,19) or in Escherichia coli (10,13), merodiploid formation in this system also requires the presence of a particular marker. For the B. subtilis strains, this is a tryptophan marker (trpE26).…”