Studies on the physical linkage of antibiotic resistance markers to ribosomal RNA genes in Bacillus subtilis

Ribosomal RNA genes in Bacillus subtilis. Evidence for a cotranscription mechanism

The analysis of the transcriptional mechanism of the ribosomal RNA genes in Bacillus subtilis was undertaken by a study of the rRNA chain elongation in the presence of rifampicin. The residual RNA synthesis after the addition of rifampicin and [3H] uridine to exponentially growing cells has shown that 56% of the radioactivity incorporated into total RNA belongs to the unstable fraction and 44% to the fraction containing mature rRNA and tRNA. Such study allowed an estimation of the half-life of messenger RNAs as being approximately 2 min. The analysis of the transcription pattern of the ribosomal RNA genes, as measured by the amount of radioactivity found in the ribosomal subunits, was complicated by a contamination of the 30 S subunits by 50 S subunits. A contamination of approximately 15% was estimated by polyacrylamide gel electrophoresis and competitive hybridization. The ratios of incorporated radioactivity at zero time when drug and label were concomitantly added ranged between 5.4-6.0, after correction for this contamination. The decay of the 23 S rRNA followed a straight line which became parabolic in its final portion. These results, and theoretical considerations on the lag of rifampicin action and on the variance of the specific activity of the nucleotide pool at the very early times of the experimental observation, favor the interpretation that the 16 and 23 S rRNA genes in B. subtilis belong to the same transcriptional unit, being cotranscribed, in that order, by the same molecule of RNA polymerase. The transcriptional times of the 16 and 23 S rRNA genes were estimated as being 30 and 60 s, respectively.

Location of the SPO2 attachment site and the bryamycin resistance marker on the Bacillus subtilis chromosome

The attachment site on the Bacillus subtilis chromosome for the lysogenic bacteriophage SPO2 has been mapped by PBS1-mediated transduction and was found to be between spc-2 and lin-2, showing 90% linkage to the former and 30% linkage to the latter marker. In the course of these studies the bry-2 marker was mapped between the cysA14 and str-1 loci.

Chromatographically fractionated complementary strands of Bacillus subtilis deoxyribonucleic acid: transformation of hybrids

The annealing properties as measured by the restoration of transforming activity and hypochromicity of methylated albumin-kieselguhr (MAK)-fractionated complementary strands of Bacillus subtilis deoxyribonucleic acid (DNA) are presented. Temperature-absorbance measurements performed on annealed mixtures of various L and H strand fractions indicated the existence of a complementarity gradient between the two MAK peaks. The markers purA16, leu-8, metB(5), thr-5, and the linked marker hisB(2)-try-2 exhibited different bimodal distributions on MAK columns. The transforming efficiency of heteroduplex mixtures, prepared by cross-annealing resolved complementary strands of wild-type and recipient DNA, was compared. The transforming efficiency of the wild-type L and H strands was equal in one preparation and unequal in a second preparation. It was found that in the second strand preparation the heteroduplex DNA containing the H strand from wild type was more efficient for all of the markers tested. The variations in transforming efficiencies of the complementary strands in heteroduplex molecules reported here and by others are due in part to strands of unequal length and probably to the self-annealing property of the H strands. At present, no conclusion could be made regarding the existence of strand selection bias during integration of donor DNA in competent B. subtilis cells.