IS THERE A HUMAN [PSI]

The yeast Sup35p protein which is responsible for. the [psi] phenotype , is a GTP-binding protein involved in translation termination. It was suggested recently that the [psi] determinant has prion-like properti es that were localized in the 114 N-terminal amino acids of the protei n. In this study, we show that the 5' end of the human SUP35 gene open reading frame is longer than previously reported by 138 codons. This N-terminal sequence presents similarities with the N-terminus of S.cer evisiae Sup35p protein, involved in [psi] maintenance By transfection of human cells and Western blotting we demonstrate that translation is initiated at the first AUG encountered at the 5' end of the human SUP 35 gene. The longest form of the protein, which contains the N-termina l extension, is the major form of Sup35p protein in non transfected ce lls. Moreover an analog of the long form of Sup35p protein is found in various mouse tissues. We suggest that the protein encoded by SUP35 g ene could have, at least in human, the properties described for the ye ast [psi] element.