A Baculovirus anti-apoptosis gene homolog of the Trichoplusia ni granulovirus

An inhibitor of apoptosis (iap) gene homolog (Tn-iap) of the Trichoplusia n i granulovirus (TnGV) was cloned, sequenced and mapped on the genome of TnG V. Tn-iap encoded a protein (Tn-IAP) of 301 amino acids with a predicted mo lecular mass of 35 kDa. The Tn-IAP contained the two sequence motifs, BIRs and RING finger, characteristic of IAP proteins, and shared identities of 2 1-27% and similarities of 28-53% with IAP proteins of Cydia pomonella GV (C p-IAP), Orgyia pseudotsugata multinucleocapsid nucleopolyhedrovirus (MNPV) (Op-IAP1, 3), Autographa californica MNPV (Ac-IAP1), Bombyx mori NPV (Bm-IA P1), Lymantria dispar MNPV (Ld-IAP3) and Buzura suppressaria single nucleoc apsid NPV (Bs-IAP1). However, Tn-IAP shared no significant homology with ba culovirus IAP2 proteins. Using an antisense Tn-iap probe, two major transcr ipts of approximately 800 nt and 1600 nt were detected by Northern blot ana lysis of RNA extracted from the fat body of T. ni larvae infected with the TnGV. Unlike Cp-IAP and Op-IAP3, however, Tn-IAP did not rescue virion occl usion in SF21 cells infected with a p35-deficient AcMNPV mutant. Tn-IAP's s ynthesis in vivo but failure to rescue p35-deficient AcMNPV in SF21 cells s uggests it is a functional IAP that is only effective in certain cell types .