Nucleic Acids Research, 1984, Vol. 12, No. 23 8987-9007
© 1984
MOLECULAR BIOLOGY |
Trasiocation affects normal c-myc promoter usage and activates fifteen cryptic c-myc transcription starts in plasmacytoma M603
Department of Biological Chemistry, School of Medicine and the Molecular Biology Institute, University of California Los Angeles, CA 90024, USA
Received August 13, 1984. Revised November 9, 1984. Accepted November 9, 1984.
Plasmacytoma M603 contains one normal, nontranslocated c-myc gene and one translocated c-myc gene 1n which c-myc exon l is juxtaposed with the immunoglobulin heavy chain enhancer and c-myc exons 2 and 3 are juxtaposed with Ca. We find that steady-state c-myc RNA levels are 2–4 fold elevated in M603 relative to normal liver or spleen and that these transcripts originate predominantly if not exclusively from the translocated c-myc gene. Although both promoters on the nontranslocated c-myc gene are repressed, the proximal promoter, Pl, is active on the translocated 5' c-myc region which is juxtaposed with the immunoglobulin heavy chain enhancer. The 3' portion of the translocated c-myc gene is transcribed from fifteen cryptic start sites and spliced at aberrant donor and acceptor splice sites, thereby generating a mixture of transcripts with different, abnormal 5' untranslated regions. Although the reason that translocation activates the cryptic c-myc starts in M603 is not completely understood, we show that truncation of the c-myc gene is not sufficient to activate cryptic transcription sites.