Abstract
EM examination of molecular hybrids between SV-40 DNA, that was cleaved with EcoRI and then digested with exonuclease III, and 16S or 19S mRNA produced late during the viral infection cycle indicated that each of these mRNA contained a 5''-terminal leader sequence that was encoded in the viral genome at about map position 0.71-0.75. Hybridization of each of these mRNA to viral DNA immobilized on nitrocellulose filters supported the EM observations.