Poly(A) polymerase I (PAP I), the pcnB gene product, is the main enzyme responsible for RNA polyadenylation in Escherichia coli. Polyadenylated RNA molecules are rapidly degraded by a multiprotein complex called RNA degradosome. Here we demonstrate that apart from its presence in cytosol, PAP I is also localized in cellular membrane. Although this observation might appear surprising, it was demonstrated recently by others that E. coli RNA degradosome is also associated with the cytoplasmic membrane. Moreover, we show that development of single-stranded RNA bacteriophages MS2 and Q beta, but not that of single-stranded DNA bacteriophage M13, is more efficient in the pcnB mutant relative to an otherwise isogenic pcnB(+) host. (c) 2005 Elsevier Inc. All rights reserved.