The nucleotide sequence of the DNA of maize streak virus (MSV) has been determined. The data were accommodated into one DNA circle of 2687 nucleotides, in contrast to previously characterised geminiviruses which have been shown to possess two circles of DNA. Comparison of the nucleotide sequences of the DNA of MSV with those of cassava latent virus (CLV) and tomato golden mosaic virus (TGMV) showed no detectable homology. Analysis of open reading frames revealed seven potential coding regions for proteins of mol. wt. greater than or equal to 10 000, three in the viral (+) sense and four in the complementary (‐) sense. The position of likely transcription signals on the MSV DNA sequence would suggest a bidirectional strategy of transcription as proposed for CLV and TGMV. Nine inverted repeat sequences which have a potential of forming hairpin structures of delta G greater than or equal to ‐14 kcal/mol have been detected. Three of these hairpin structures are in non‐coding regions and could be involved in the regulation of transcription and/or replication.

Three RNA transcripts encoded by maize streak virus DNA were detected in polyadenylated RNA from virus-infected maize leaves.Two of the transcripts, a major 0.9kb and a minor 1.05kb RNA, were mapped on the virion (+) sense DNA and the other minor transcript of 1.2kb was mapped on the complementary (-) sense DNA, demonstrating that transcription of MSV DNA was bidirectional.The two virion sense transcripts were 3' coterminal at nucleotide 1114 but had 5' termini at nucleotides 2682 and 163 respectively. Virus-specific polyadenylated RNA translated in vitro to produce a 28,000MW polypeptide, specifically immunoprecipitable by antiserum raised against whole virus. The mRNA for this protein was mapped by hybrid-arrested translation to the long open reading frame in virion sense DNA whose potential amino acid composition, calculated from nucleotide sequence data, closely agreed with that determined experimentally for the coat protein.

We have isolated, from maize streak virus (MSV) preparations, a population of ‘nested’ DNA molecules. These molecules have ribonucleotides covalently linked to the DNA species’ discrete 5′ deoxyribonucleotide terminus. The major species has a DNA sequence of 80 nucleotides which is complementary to a region 5′ of two hairpin structures on the MSV genome, almost exclusively in an intergenic region. These molecules have been used to prime the synthesis in vitro of a complementary strand to virion DNA, initiating this reaction at one site on the genome.

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