DNA sequence analysis of the inverted terminal repeats of a non-oncogenic avian adenovirus.

In a l l adenovlruses (AV) studied to date the DNA possesses a unique inverted terminal repeat (ITR) of the form abc . . . o'b a .Although the repeat sequences are t h o u g h t t o have a r o l e in DNA r e p l i c a t i o n t h e i r e x a c t f unc t i on i s unknownO). Terminal DNA fragments of fowl adenovirus type 10 </ere iden t i f i ed by limited Bal 31 digest ion of genomic DNA prior to restr ict ion enzyme cleavage and gel electrophoresis.The terminal fragments iden t i f i ed were further confirmed by ext rac t ing the viral DNA with the terminal protein intact , as previously described (2).The sequence of the non-oncogenic fowl adenovirus type 10 ITR i s presented ( F i g . 1 ) , compar i son w i t h o t h e r AV ITRs r e v e a l s s eve ra l I n t e r e s t i n g features.Firstly the length of the ITR of this non-oncogenic avian AV i s no l e s s than that of the ITR from the highly oncogenlc fowl AV type l(CELO).This i s In direct contrast to r e s u l t s reported for human AV where the length of the ITR Increases with the Increasing oncogeniclty of the virus type ( l ) . T h i s result suggests t ha t , at l e a s t In avian AV, the length of the ITR is not r e l a t ed to oncogenicity.Secondly, unlike CELO and mammalian AV, this virus does not possess the sequence ATAATA at position 9-Tt within the ITR.This sequence is thought to be a recognition sequence for the precursor of the terminal repeat protein which is Involved In the Init iation of DNA replication (3).However, the ITR of t h i s type 10 avian AV does possess the sequence ATATA at position 10-1t, suggesting that this abbreviated form may be su f f i c i en t for recognit ion by the t e rmina l p r o t e i n precursor.Thirdly the l e f t and r i gh t ITR of the type 10 avian AV, unlike CELO virus, end with the sequence ACGT an abbreviated form of the TGACCT sequence found In the same or similar position in human AV types 2, 3, 5, 7 and 12(1).