Plant Pathology Department


Date of this Version



Published in Journal of Biological Chemistry 265:14 (May 15, 1990), pp. 7779–7786. Copyright © 1990 by The American Society for Biochemistry and Molecular Biology, Inc. Used by permission.


The 5’ end of tobacco mosaic virus (TMV) genomic RNA is capped with 7- methylguanosine. A virus-coded polypeptide with guanylyltransferase activity has been investigated. This enzyme is responsible for forming the 5’→5’ linkage of guanosine 5’-monophosphate to the 5’- diphosphate of an acceptor RNA, thereby forming the cap. A critical step in the mechanism for cap formation in the eukaryotic nucleus is for guanylyltransferase to bind covalently to guanosine 5’- monophosphate with the hydrolysis of pyrophosphate when guanosine 5’- triphosphate is the substrate. The TMV 126-kilodalton protein, which is most probably a component of the TMV replicase, was found to have this activity. The mechanism of this reaction has been characterized biochemically.