Biomedical subjects
Publications and source records attributed to C Backendorf.
30-S ribosomal subunits of Escherichia coli form a stable complex with MS2 RNA or Q beta RNA at 37 degrees C in the absence of initiator tRNA. The complex functions as a precursor of initiation since it can enter the ribosome cycle in the presence of inhibitors of de novo initiation.
The deoxyoctanuclotide (5'-3')d(A-A-G-G-A-G-G-T), which is complementary to the 3' end of 16-S RNA, inhibits the formation of the complex between the 30-S subunit and MS2 RNA described in the preceding paper. If the complex is preformed, the octanucleotide cannot prevent entry of the complex into the ribosome cycle upon supplementation with the components for protein synthesis. The subunit . MS2-RNA complex is unable to bind the octanucleotide. It is concluded that in the subunit . phage-RNA initiation precursor the 16-S terminus is base-paired with a complementary MS2 RNA sequence. Edeine, aurintricarboxylic acid and antibodies against ribosomal protein S1 prevent the association of phage RNA with 30-S subunits. These compounds do not, however, inhibit the binding of (5'-3')d(A-A-G-G-A-G-G-T) to 3-S subunits. It is concluded that formation of the complex between MS2 RNA and 30-S subunits does not depend solely on the Shine and Dalgarno base-paring reaction.
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The coding sequence of the uvrA gene from Escherichia coli has been fused to the early promoter, enhancer and origin of replication of the simian virus SV40, and was supplemented with splicing and polyadenylation sites arising from the same virus. Introduction of this hybrid gene into simian cos-1 cells results in the synthesis of a full length UvrA protein (114 kD) which has retained its ability to bind to single-stranded DNA.
The Escherichia coli single-stranded DNA binding protein (SSB) is implicated in DNA replication, recombination and repair. On the chromosome, the ssb gene is located adjacent to the excision repair gene uvrA, but the two genes are transcribed in opposite directions. uvrA has been shown to be part of the E. coli SOS system by introducing Mud(Ap, lac) insertions distal to the regulatory region of the gene in the chromosome. Recent investigations suggest that SSB is also involved in the SOS response. However, because the SSB protein is essential to the cell, the inducibility of the ssb gene cannot be investigated by the insertion method. Therefore, we used plasmids harbouring the regulatory region of ssb fused to the galK structural gene, while leaving an intact ssb gene in the chromosome. We show here that expression of the ssb gene is dependent on two promoters of which one is damage inducible. Evidence is presented that the divergently transcribed ssb and uvrA genes are controlled by a common LexA binding site.