RNA-DNA hybridization experiments were used to yield information as to the number of cistrons coding for different classes of RNA in Bacillus subtilis. It was found that there are three to four genes for 5 s RNA, nine to ten genes for 16 and 23 s RNA and approximately 40 for tRNA. The localization of DNA base sequences complementary to these RNA species has also been studied, using a modified density transfer method with germinating B. subtilis spores. Spores were germinated in D2O medium and DNA was isolated at various times. Hybrid and light DNA molecules were fractionated by preparative CsCl density gradient centrifugation and transforming activity for various genetic markers, as well as the ability to hybridize with the different species of rRNA and tRNA, was assayed. Our results permit the following conclusions: 1. (1) About 60 to 80% of the 16 and 23 s rRNA and tRNA cistrons are located to the left of purB6† † Abbreviations used: Genetic markers, pur, arg, leu, met, his and ura denote mutations affecting the synthesis of purine, arginine, leucine, methionine, histidine and uracil, respectively; ery, str and mic designate mutations conferring resistance to the antibiotics erythromycin, streptomycin and micrococcin, respectively. SDS, sodium dodecyl sulfate; MAK, methylated albumin kieselguhr. on the B. subtilis chromosome. The remaining 20 to 40% of these genes are located in the terminal portion of the chromosome. The major group thus includes six to eight cistrons for 23 and 16 s RNA and 25 to 35 for tRNA. 2. (2) The cistrons coding for 5 s ribosomal RNA are distributed in the same way. About 60 to 80% (two to three cistrons) are located to the left of purB6 and the remainder in the terminal portion of the chromosome. 3. (3) The average map position of the DNA sequences complementary to the RNA species and of the transforming markers in this region occur in the order: str, 23 s RNA, 16 s RNA, tRNA, purB6. The average map position of the DNA sequences complementary to 5 s RNA is close to those of the 23 and 16 s RNA loci. 4. (4) The kinetics of replication of the rRNA loci suggest that cistrons coding for 5, 16 and 23 s rRNA are located on both sides of str and are therefore intermingled with one another. The position of tRNA cistrons relative to str is less clear.
All Science Journal Classification (ASJC) codes
- Structural Biology
- Molecular Biology