Characterization of UL1, a member of the human cytomegalovirus RL11 gene family

Resumen

We have investigated the previously uncharacterized human cytomegalovirus (HCMV) UL1 open reading frame (ORF), a member of the lately evolving HCMV RL11 gene family. UL1 is HCMV specific; absence of UL1 in chimpanzee CMV (CCMV) and sequence analysis studies suggests that UL1 may have originated by duplication of an ancestor gene from the RL11-TRL-cluster (TRL11, TRL12 and TRL13). Sequence similarity searches against human immunoglobulin (Ig) containing proteins revealed that HCMV pUL1 shows significant similarity to the cellular carcinoembrionic antigen related (CEA) protein family N- terminal Ig domain, which is responsible for CEA ligand recognition. Northern blot analysis revealed that UL1 is transcribed during the late phase of the HCMV replication cycle, both in fibroblast-adapted and endotheliotropic strains of HCMV. We characterized the protein encoded by an HA-tagged UL1 in the AD169-derived HB5 background. UL1 is expressed as a 224 amino acid type I transmembrane glycoprotein which becomes detectable not earlier than 48 h to 72 h post infection. In infected human fibroblasts, pUL1 co-localized at the cytoplasmic site of virion assembly and secondary envelopment together with TGN-46, a marker for the trans-Golgi network, and viral structural proteins including envelope glycoprotein B and tegument phosphoprotein pp28. Furthermore, analysis of highly purified AD169 UL1-HA epitope tagged virions revealed that pUL1 is a novel constituent of the HCMV envelope. Importantly, deletion of UL1 in HCMV TB40/E resulted in a reduced growth in a cell type-specific manner, suggesting that pUL1 may be implicated in regulating HCMV cell tropism. Palabras Clave de la Tesis: cytomegalovirus, virion, cell tropism, glycoprotein, gene expression