IDENTIFICATION OF A NOVEL CELLULAR TPR-CONTAINING PROTEIN, SGT, THAT INTERACTS WITH THE NONSTRUCTURAL PROTEIN NS1 OF PARVOVIRUS H-1

The nonstructural protein NS1 of autonomous parvoviruses is essential for viral DNA amplification and gene expression and is also the major cytopathic effector of these viruses. NS1 acts as nickase, helicase, a nd ATPase and upregulates P38-driven transcription of the capsid genes , We report here the identification of a novel cellular protein that i nteracts with NS1 from parvovirus H-1 and which we termed SGT, for sma ll glutamine-rich tetratricopeptide repeat (TPR) containing protein. T he cDNA encoding full-length SGT was isolated through a two-hybrid scr een with, as bait, the truncated NS1dlC69 polypeptide, which lacks the C-terminal transactivation domain of NS1, Full-length NS1 and SGT int eracted in the two-hybrid system and in an in vitro interaction assay. Northern blot analysis revealed one major transcript of about 2 kb th at was present in all rat tissues investigated. Rat sgt cDNA coded for 314 amino acids, and the protein migrated in sodium dodecyl sulfate-p olyacrylamide gel electrophoresis with an apparent molecular mass of 3 4 kDa, SGT could be detected in both the nucleus and the cytoplasm of rat cells, as determined by indirect immunofluorescence analysis and W estern blotting of fractionated cellular extracts with an affinity-pur ified antiserum raised against recombinant SGT (AC1.1). In H-1 virus-i nfected rat and human cells, compared to mock-infected controls, diffe rences in the migration of SGT polypeptides were revealed after Wester n blot analysis of total cellular extracts. Moreover, the transient ex pression of NS proteins was sufficient to induce SGT modification, The se results show that cellular SGT, which we have identified as an NS1- interacting protein, is modified by parvovirus infection as well as NS expression.