THE 5'-END OF THOGOTO VIRUS (ORTHOMYXOVIRIDAE) MESSENGER-RNAS ARE HOMOGENEOUS IN BOTH LENGTH AND SEQUENCE

Thogoto (THO) virus is a tick-borne member of the Orthomyxoviridae who se genome consists of six segments of linear, negative sense, single-s tranded RNA. To gain insight into the mechanism by which viral mRNA tr anscripts are initiated, poly(A)(+) RNA isolated from THO virus-infect ed cells was characterized by (i) primer extension experiments, (ii) i mmunoprecipitation studies with an anticap monoclonal antibody, (iii) direct sequencing analysis of the isolated RNA, and (iv) cloning and s equencing of individual mRNA molecules. The results indicated that THO virus mRNAs are capped and homogeneous in both length and sequence at their 5' end. These findings contrast with the situation found in all other segmented, negative sense or ambisense, single-stranded RNA vir uses so far analyzed in which the 5' ends of viral mRNAs are heterogen eous in length and sequence. These results are discussed in terms of t he mechanism used by THO virus to initiate mRNA synthesis.