No abstract

Human cytomegalovirus (HCMV) is a herpesvirus with a genome of 230 kilobases (Kb) encoding about 200 genes. Although infection is generally innocuous, HCMV causes serious congenital and neonatal disease, and is a dangerous opportunistic pathogen in immune-deficient individuals. We have identified a family of three HCMV genes which encode polypeptides containing seven putative membrane-spanning domains, and a series of well-defined motifs characteristic of the rhodopsin-like G protein-coupled receptors (GCRs). By these criteria all three of the HCMV sequences are homologous to cellular GCRs. Members of this receptor family function in visual signal transduction, regulation of homeostasis, and development, and include known and potential oncogenes. These receptors are activated by photons or small molecules such as neurotransmitters, and glycoprotein hormones. The finding of viral-encoded GCR homologues implies a further level of complexity in the interactions between HCMV and its host, and may provide a potential pathway for virally transformed cell proliferation. Their identification could permit the development of a novel class of antiviral drugs analogous to beta-adrenergic receptor antagonists.

Nodulin‐35, a protein specific to soybean root nodules, was purified under non‐denaturing conditions (DEAE‐cellulose followed by Sephacryl S‐200 chromatography) to homogeneity. The holoprotein showed uricase (EC 1.7.3.3) activity. Analytical ultracentrifugation under non‐denaturing conditions revealed a molecule of 124 kd, S°20W = 8.1; however, under denaturing conditions a value of 33 kd, S°20W = 1.9, was obtained. This indicated that nodulin‐35 is the 33‐kd subunit of a specific soybean root nodule uricase (uricase II) and that the enzyme contains four similar subunits. The native molecule contains ˜1.0 mol Cu2+ per mol, has an isoelectric point of ˜9.0 and a pH optimum for uricase activity at 9.5. Uricase activity found in young uninfected soybean roots is due to another form of enzyme (uricase I) which is of ˜190 kd, has maximum activity at pH 8.0 and does not contain any subunit corresponding in size to nodulin‐35. Uricase I, also present in young infected roots, declines at a time when nodulin‐35 appears. Monospecific antibodies prepared against uricase II (nodulin‐35) showed no cross‐reactivity. Uricase II was localized in the uninfected cells of the nodule tissue. These results are consistent with the concept that a nodule‐specific ureide metabolism takes place in peroxisomes of uninfected cells, and suggest the participation of uricase II in this pathway.

Human cytomegalovirus particles contain a phosphoprotein of 150,000 (ppl50) apparent molecular weight in their matrix; the protein appears particularly reactive in Western blot analyses with human antisera. The gene for ppl50 was mapped by screening a bacteriophage lambda gtll cDNA expression library with monospecific rabbit antisera. Subsequent hybridization of cDNA with cosmid and plasmid clones containing the human cytomegalovirus strain AD169 genome mapped the gene to HindIII fragments J and N. The gene is transcribed into a late 6.2-kilobase RNA. The nucleotide sequence of this region was determined, and a transcription initiation site and two polyadenylation sites of an abundant transcript were located by primer extension and nuclease protection experiments. The reading frame for ppl50, deduced from computer analyses, gives rise to a polypeptide of 1,048 amino acids in length; protein secondary structure analysis revealed multiple n-pleated sheets in hydrophilic clusters, providing a possible explanation for the immunogenic properties of the polypeptide.