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Figure 1 | Retrovirology

Figure 1

From: Avian myeoloblastosis virus (AMV): only one side of the coin

Figure 1

Schematic organization and expression the MAV and AMV proviral genomes. The MAV RNA genome that is contained in infectious particles is retrotranscribed by RT and viral proteins are expressed from the proviral double stranded DNA copy of the viral genome, which is integrated into the host genome. The structural glycoproteins (MA, p10, CA, NC, PR) and reverse transcriptase (POL) are produced by post translational processing of the gag-pol polyprotein precursor, which is expressed in the form of a bicistronic message (n672-n2777, n2780-n5482) from the proviral genome. The envelope protein is made from spliced mRNA species that join 17 aminoterminal amino acid residues to the env ORF that begins at nucleotide 5370 of MAV and overlaps the 3' end of the pol gene, encoding the integrase activity (IN). MAV infected cells contain the viral RNA genome, and both the subgenomic gag-pol precursor and env mRNAs. Cell-derived v-myb oncogenic sequences are transduced by AMV. Recombination of the truncated c-myb c-DNA copy with the MAV proviral genome occurred within the pol and env genes of MAV at nucleotides 5372 and 7121, respectively in the proviral DNA of MAV-1. The env splice acceptor localized upstream to the 5' proximal recombination point in MAV DNA, is used to join the v-myb ORF to the 17 aminoterminal residues of the gag protein. As a consequence of the v-myb integration the AMV is replication defective because it lacks the gag and pol proteins. Only the genomic viral RNA and the v-myb RNA are expressed from the proviral AMV. The high degree of conservation between the pol coding sequences which are contained in the MAV genome and the portion of pol sequences contained in the AMV genome, suggest that recombination between AMV and MAV may occur at this level, and result in the production of pol proteins from both genomes. However, this has not been demonstrated as yet. top: MAV proviral genome. Solid boxes represent the LTR sequences which are generated during the process of proviral DNA synthesis and integration. The gag-pol polyprotein precursor comprises gag sequences (stipled box) and pol sequences (striped box). Proteolytic cleavage of the precursor occurs at position corresponding to codon 2777–2780. The two black boxes represent the coding sequences of the envelope protein that are joined by splicingw which occurs between the gag splice donor at nucleotide 689 and the splice acceptor at position 5370 in the pol sequences. Bottom: proviral AMV genome. The v-myb coding sequences are made of a part of gag (black box) and c-myb derived sequences (hatched box). Arrows indicate the points of recombination of the c-myb derived sequences in the MAV genome.

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