FUNCTIONAL-ANALYSIS OF FILAMENTOUS PHAGE F1 MESSENGER-RNA PROCESSING SITES

The abundant mRNAs used as templates for synthesis of filamentous phag e fl proteins are a combination of primary transcripts and 3' products of processing. The processing steps are mediated by host endoribonucl eases. One of the enzymes implicated in fl mRNA processing is RNase E, the only endonuclease thus far shown to have a global role in mRNA de cay. By establishing the temperature-sensitive phenotypes of RNase E m utants and then inducing a transcription unit bearing cloned fl proces sing sites, we show that RNase E is required for production of at leas t three of the processed RNAs. Using in vivo processing assays, we als o test directly the regions implicated genetically in previous work to contain the processing sites. The sites function as discrete domains in a number of transcription units, show little influence of translati on, but appear to have increased activity at the 5' terminus of an mRN A. From their functional properties, we suggest that the known process ing sites from phage fl that are dependent on RNase E may be represent ative of relatively late steps in me-dependent cleavage pathways.