Human and simian adenoviruses: phylogenetic inferences from analysis of VA RNA genes.

Adenovirus VA RNA genes have primary sequence constraints due to internal promoter regions and a high degree of secondary structure in the RNA product. To determine the relationships between human and simian adenoviruses, the VA RNA genes of several primate adenoviruses were characterized and compared to those sequences already published. Human adenoviruses of subgenera A, B:2, and F have only one VA RNA gene, whereas human adenoviruses of subgenera B:1, C, D, and E have two. The genomes of 12 monkey adenoviruses were found to have only one VA RNA gene, whereas the genomes of six representative chimpanzee adenoviruses were each found to have two VA RNA genes. Phylogenetic analysis of representative VA RNA gene sequences individually, irrespective of their strain of origin or partnering VA RNA gene, gave the following inferences. (1) The single VA RNA genes of human adenovirus subgenera A and F are most closely related to those of monkey adenoviruses. (2) The VA RNAI genes of human adenoviruses in subgenera B:1, D, and E, and also the single VA RNA genes of subgenus B:2 probably diverged from a common ancestral VA RNA gene. (3) This ancestral gene most likely reduplicated to give the precursor of all VA RNAII genes, the evidence for which has been almost totally lost in subgenus B:2 adenoviruses. (4) The two VA RNA genes of human subgenus C adenoviruses are relatively distant from each other phylogenetically. Since the Ad2 and Ad5 VA RNAI genes have a higher identity to the single VA RNA gene of SAV13 (SV36) than to those of any of the other human adenoviruses, these genes may have entered the human subgenus C adenovirus genome by substitution involving recombination with a simian adenovirus. The results of this study suggest that a renewed appraisal of VA RNA function in adenoviruses other than Ad2 and Ad5 may be necessary.