c-erbB activation in avian leukosis virus-induced erythroblastosis: multiple epidermal growth factor receptor mRNAs are generated by alternative RNA processing.

Avian leukosis virus-induced erythroblastosis results from the specific interruption of the host oncogene, c-erbB, by the insertion of an intact provirus. This insertion results in the expression of two size classes (3.6 and 7.0 kilobases [kb]) of truncated c-erbB transcripts which are initiated in the 5' long terminal repeat of the integrated provirus. Through sequence analysis of erbB cDNA clones we have previously shown that the 3.6-kb activated erbB mRNA contains portions of viral gag and env genes fused to c-erbB sequences (T.W. Nilsen, P.A. Maroney, R.G. Goodwin, F.M. Rottman, L.B. Crittenden, M.A. Raines, and H.-J. Kung, Cell 41:719-726, 1985). In this report we show that the 7-kb mRNA differs from the shorter activated c-erbB mRNA in the length of its 3' untranslated sequence such that the longer mRNA has an extremely long (4.3 kb) 3' untranslated sequence. Additionally, we demonstrate that activated c-erbB mRNA precursors can be processed by alternative splicing to yield mRNAs with viral gag sequences fused directly to c-erbB sequences. Finally, blot hybridization evidence suggests that the two size classes of activated c-erbB mRNA in erythroblastic tissue represent truncated versions of the two c-erbB mRNAs present in normal tissue.