VA RNAs from avian and human adenoviruses: dramatic differences in length, sequence, and gene location

Abstract

Human adenoviruses encode low-molecular-weight RNAs, so-called VA RNAs, which are transcribed by RNA polymerase III. These RNAs are required for an efficient translation of viral mRNAs late after infection. The genes for the VA RNAs in the genome of CELO virus were mapped and characterized. The results showed a number of surprising differences between CELO virus and human adenovirus type 2 (Ad2). Thus, the CELO virus genome encoded only one VA RNA species, in contrast to human Ad2, which encoded two distinct species. The VA RNA from CELO virus was much shorter than the Ad2 VA RNAs (90 nucleotides compared with 160 nucleotides), and there existed no detectable primary sequence homology between them. The predicted secondary structure of CELO virus VA RNA was, however, similar to that of the Ad2 VA RNAs, implying that the folding rather than the primary sequence was the important feature for biological activity. CELO VA RNA also stimulated translation in a transient expression assay, as did the Ad2 counterparts, albeit with a much lower efficiency. The location of the gene for CELO VA RNA also differed from all previously characterized serotypes, suggesting that the genome organization of avian and human adenoviruses are different. Finally, termination of CELO VA RNA transcription occurred in a TTATT sequence which is unique as a stop signal for RNA polymerase III transcription.

Comparative analysis of the structure and function of adenovirus virus-associated RNAs

“…Viral DNA isolated from two nonhuman adenoviruses, SA7 and CELO virus, encode VA RNAs which can be synthesized by Pol III in vitro. The SA7 and CELO virus VA RNA genes have been mapped by the nuclease protection technique, and they have been shown to substitute partially for Ad2 VA RNA, in a functional assay (41,42). Thus, neither the Ad7 nor Adl2 VA RNAs have been shown to prevent DAI activation, and the SA7 and CELO virus VA RNAs have not been detected in vivo.…”

“…2). CELO virus, however, has its single VA RNA gene located on the r strand of the genome and yields two VA RNAs because of inefficient 3'-end formation at the proximal termination site (41,44). Apart from a single assignment (nucleotide 30 of Ad7…”

“…Unlike the mammalian genes, however, the avian VA RNA gene is located at 90 map units and is transcribed in the leftward direction. Nevertheless, CELO virus VA RNA appears to function like Ad2 VA RNAJ, albeit considerably less efficiently (41). Thus, VA RNA genes are carried by all the adenovirus serotypes examined, although they differ in number, sequence, location, and possibly function.…”

“…A similar organization seems to exist in Ad7, a representative of group B of the human adenoviruses (15,58), but the group A virus Adl2 and simian adenovirus type 7 (SA7) apparently contain only a single VA RNA gene at this locus (16,42,69). Chicken adenovirus type I (also known as CELO virus) carries a gene encoding two shorter VA RNAs which are overlapping transcripts from a single gene (41). Unlike the mammalian genes, however, the avian VA RNA gene is located at 90 map units and is transcribed in the leftward direction.…”

Xenogenic Adenoviral Vectors

“…Also in the central core of HAdVs are one or two copies of VA RNA genes [52]. Except for PAdV3 [46] and SAdVs [53], these are not present in xenogenic mastadenoviruses or OAdV7 [54], but a single copy is present near the right-hand end of FAdVl [55] and DAdVl ( Fig. 1) [23,48].…”