Activation of major histocompatibility complex class I mRNA containing an Alu -like repeat in polyoma virus-transformed rat cells

Class I genes of the major histocompatibility complex (MHC) appear to be activated in mouse cells transformed by the DNA tumour virus simian virus 40 (SV40) 1 . Conversely, suppression of MHC class I genes has been reported in adenovirus-12-transformed baby kidney rat cells 2 . We have now investigated the expression of genes encoded by the rat MHC locus in rat fibroblast cells transformed by polyoma virus (Py). Using a mouse genomic H–2 clone as a probe in Northern transfer hybridization analysis, we have observed a high level of expression of rat MHC class I messenger RNA in all the transformed rat cell lines analysed. The class I 1.6-kilobase (kb) mRNA activated in Py-transformed rat cells appears to contain an Alu -like type II repeat element, as the same 1.6-kb mRNA is detected using either the H–2 class I sequence or a repetitive Alu -like type II element as a probe. High levels of heterogeneous poly(A) + transcripts of 0.5–0.8 kb are also observed in Py-transformed rat cells using probes containing an Alu -like type II repetitive element.