| Popis: |
Infection of the Escherichia coli RNA-processing mutant rne with the bacteriophage strain T4Δ27 (a deletion in the transfer RNA region that leaves intact only three of the ten final RNA molecules) results in a reduced accumulation of the three mature RNAs: species 1 (a small RNA of unknown function), tRNALeu and tRNAGln, as well as an accumulation of two new RNAs: 10·1 S and p2Sp1 (a precursor of species 1). Structural analyses of these molecules showed that 10·1 S RNA contains tRNAGln, tRNALeu and species 1 RNA (in this order), while p2Sp1 is similar to the distal part of the 10·1 S RNA and contains only species 1 RNA. The 10·1 S and p2Sp1 molecules share a common 3′ terminus, which is apparently formed by termination of transcription. Using cell extracts, in which RNase E was inactivated, as the source of processing enzymes and 10·1 S RNA as the substrate, production of the final three RNA molecules took place, albeit at lower rates. Heating extracts even at relatively high temperatures did not prevent the RNase E− extracts from processing p2Sp1 to species 1. These observations can be explained in at least two ways: RNase E is directly involved in the production of the three final RNA molecules, but there is at least one other enzyme, which either normally or only in the absence of RNase E carries out similar cleavages; alternatively RNase E is involved indirectly in the processing of bacteriophage T4 10·1 S RNA by affecting the activity of at least one other RNA processing enzyme. We prefer the second possibility. Thus, these studies demonstrate the existence of new T4 tRNA precursors and host RNA-processing enzyme(s), and lead to a new concept in RNA processing, whereby one enzyme can affect very drastically the function of another enzyme. |
