APPROPRIATE EXPRESSION OF FILAMENTOUS PHAGE F1 DNA-REPLICATION GENE-II AND GENE-X REQUIRES RNASE E-DEPENDENT PROCESSING AND SEPARATE MESSENGER-RNAS

The products of in-frame overlapping genes II and X carried by the fil amentous phage fl genome are proteins with required but opposing funct ions in phage DNA replication, Their normal relative levels are import ant for continuous production of phage DNA without killing infected Es cherichia coli hosts, Here we identify several factors responsible for determining the relative levels of pII and pX and that, if perturbed, alter the normal distribution of phage DNA species in infected hosts. Translation of the two proteins is essentially relegated to separate mRNAs, The mRNAs encoding genes II and X are also differentially sensi tive to cleavage dependent on rne, the gene encoding the only E. coli endo-RNase known to have a global role in mRNA stability. Whereas pII levels are limited at the level of mRNA stability, normal pX levels re quire transcription in sufficient amounts from the promoter for the sm aller mRNA encoding only pX.