Expression of rubella virus cDNA coding for the structural proteins.

A cDNA clone encoding the precursor polypeptide (Mr 115,000) to the nucleocapsid C (Mr 30,000) and two envelope glycoproteins E1 (Mr 58,000) and E2 (Mr 42,000-47,000) of rubella virus was inserted into a simian virus 40-derived eukaryotic expression vector. When the plasmid was introduced into COS cells, three proteins were synthesized. The expressed proteins were antigenically similar and identical in size to the authentic structural proteins of rubella virus. Expression in the presence of tunicamycin confirmed that E1 and E2 are glycoproteins. Unglycosylated E1 and E2 had Mrs of about 53,000 and 30,000, respectively. The mobility of the nucleocapsid protein was unaffected by tunicamycin. The locations of the translation start and stop codons for synthesis of the precursor to the structural proteins of rubella virus were determined by in vitro and in vivo expression studies. It was found that the first AUG codon at the 5' end of the rubella virus 24S cDNA acts as a start codon for translation. The stop codon was found to be 3183 bp from the start codon.