The first complete nucleotide sequences of two lytic Staphylococcus aureus double stranded DNA phages, 44AHJD (16 784 bp) and P68 (18 227 bp), are reported. Both are small isometric phages, with short, non-contractile tails and a pre-neck appendage. Based on their morphology, their genome size, the similarity of the encoded gene products, the type of infection and on the possession of a type B DNA polymerase, 44AHJD and P68 are allocated to the order Caudovirales, family Podoviridae, genus 'P29-like phages'. The genome of 44AHJD differs from that of P68 by a deletion spanning nucleotides 10 091 to 11 531 of the P68 genome. The electrophoretic analysis of the terminal DNA fragments of P68 DNA and P68 DNA protein complex suggested the presence of a terminal protein at either DNA end. In contrast to the lysis cassette of the P29-like phages, which is located at the end of the late operon, the lysis cassette of 44AHJD and P68 is located within the structural genes.

Phage-encoded murein hydrolases are either part of the lysis cassette or found as structural components of the phage virion. Here, we show that Staphylococcus aureus bacteriophage P68 contains a virion-associated muralytic enzyme. Protein 17 has a composite structure. The N-terminal part comprises the muralytic activity, whereas the C-terminal part is required for binding to the cell surface. A high multiplicity of infection with phage P68 caused rapid lysis, and purified protein 17 triggered premature lysis when added to S. aureus cells prior to infection with P68, suggesting that it functions to weaken the murein at the site of phage DNA entry. Protein 17 displayed activity against clinical S. aureus isolates, which are resistant to infection by phage P68, demonstrating that the protein targets surface structures distinct from the phage receptor. This broad activity spectrum of protein 17 could qualify virion-associated muralytic enzymes as attractive antimicrobials.

Mature Xenopus laevis spermatozoa are capable of binding plasmid pAPrC carrying the complete Rous sarcoma virus (RSV) DNA. Each sperm cell associates, on an average, with 70-160 molecules of the plasmid DNA in a DNase resistant form, if the spermatozoa were exposed to the DNA at a concentration of 1.0-1.4 micrograms/10(7) sperm cells. Fertilization with pAPrC-treated spermatozoa induced developmental malformations in 25-30% of embryos. Immunohistochemical analysis of tissue sections from defective animals revealed aberrations in myotomal structures, and increased expression of pp60src protein in myoblasts, neuronal tube, and epidermis. The presence of characteristic v-src and RSV-long terminal repeat (LTR) sequences in X. laevis DNA was detected by PCR analysis. Embryonic RNA hybridized with a src-specific and an RSV-LTR specific probes indicating expression of the viral DNA. Plasmid DNAs without the v-src gene (pATV9) or completely free of any RSV sequences (pBR322) did not induce any changes in embryonic development. Our results provide evidence that the pBR322-cloned DNA form of the RSV genome associates with frog sperm cells in a DNase-resistant manner suggesting internalization and may be subsequently carried into eggs during the process of artificial fertilization. Correlation between the defective morphogenesis of X. laevis and increased expression of the src gene as well as an interference of RSV DNA with the developmental programs of frog embryos are discussed.