Abstract
cDNAs coding for the E1 structural protein of the Thomas strain of RV have been cloned and sequenced. Comparisons between the predicted amino acid sequences of the E1 structural protein of other strains reveals only one unique change in the Thomas sequence at position E1155. cDNA coding for the complete E1 protein and subfragments of E1 have been expressed as glutathione-S-transferase fusion proteins in E. coli. The two smallest soluble fusion proteins from pUS1503 and pUS1509 which contain only previously identified epitopes, were used as antigens in an ELISA assay for rubella antibody screening. From the analysis of 42 human sera, the protein from pUS1503 showed a sensitivity of 53% and a specificity of 80% whereas protein from pUS1509 gives a sensitivity of 81% and specificity of 80%. The E1 and E2 proteins have been expressed in eukaryotic systems both in vitro and in vivo. In vitro expression confirmed that a bovine IgG signal peptide could substitute for the putative rubella E1 signal peptide and allow processing by microsomal membranes. Expression of an E1 variant lacking the trans-membrane anchor failed to produce detectable levels of a secreted protein in COS-1 cells even when intracellular protein was produced. To provide new data on the location of rubella E1 epitopes and to investigate the human antibody response to rubella, overlapping synthetic octameric peptides covering the E1 sequence were used in binding studies with rubella positive and negative sera. Each human sera analysed displayed a unique profile of antibody binding to specific peptides. Pooled data identified groups of peptides which consistently bound antibodies from rubella positive sera. The majority of antibody binding sites were outside the previously defined region containing four epitopes (eps1-4). The majority of sera showed no binding to eps2 and eps3.