Dugbe Nairovirus M RNA: nucleotide sequence and coding strategy.

The coding assignments of the medium-sized (M) RNA segment of the Dugbe (DUG) virus (Nairovirus, Bunyaviridae) were investigated. The complete nucleotide sequence of 4888 nucleotides (nt) contained one long open reading frame in the viral complementary RNA, extending from an AUG start codon at nt 48-50 to a stop codon at nt 4701-4703 (numbered from the 5' terminus of vcRNA). Comparison of the terminal sequences with the ends of the DUG S segment revealed sequence identity between the first nine nucleotides of both segments. No sequence homologies were found with the M segments of other members of the Bunyaviridae, or with their polypeptide products. Expression of portions of the DUG M open reading frame in Escherichia coli demonstrated the carboxyl terminal region of the M open reading frame codes for the G1 structural glycoprotein, which is the target for neutralising antibodies. Confirmation of this assignment was obtained by sequencing the amino terminus of the G1 protein. Two nonstructural glycoproteins which share epitopes with G1 were identified in virus-infected cells, one of which (85 kDa) is processed over a period of several hours to produce G1. The G2 coding region was located upstream of the G1 sequence. The region between the carboxyl terminus of G2 and the 5' end of the long open reading frame apparently encodes a nonstructural protein of about 70 kDa, which is a precursor of the G2 protein.