Differential splicing of the mouse B-myb gene.
The myb gene family consists of three members, the c-myb proto-oncogene and two myb-related genes (A-myb and B-myb), all of which encode nuclear DNA-binding proteins. Unlike c-myb, which plays a critical role in hematopoietic cells, B-myb is expressed in a large spectrum of hematopoietic as well as non-hematopoietic cells and has been implicated in the control of cell proliferation. The isolation of B-myb cDNA clones from several species has shown that B-myb shares limited homology to the so-called exon 9A of the c-myb gene. This exon is involved in differential splicing as only a subfraction of c-myb mRNA contains exon 9A sequences. The presence in the B-myb cDNA of a sequence related to the exon 9A of c-myb has prompted us to investigate whether B-myb mRNA is also spliced differentially. We here show that B-myb mRNAs containing or lacking exon 9A related sequences are present in many cell types. In contrast to c-myb, where RNA containing the exon 9A constitutes only a minor mRNA fraction, B-myb RNA containing the exon 9A related sequences is the major mRNA form. The proteins encoded by the two B-myb mRNA species are unable to activate promoters to which they bind. Curiously, both B-myb proteins differ in their ability to activate the HSP70 promoter by a myb binding-site independent mechanism; B-myb protein containing exon 9A related aminoacid sequences activates the HSP70 promoter much more potently than the B-myb protein which lacks these sequences. Our results suggest that differential splicing may be a general feature of the members of the myb family and provide first evidence for functional differences of the splice variants.
Kamano
H
H
Hans-Spemann-Laboratory, Max-Planck-Institute for Immunobiology, Freiburg, Germany.
Burk
B
B
Noben-Trauth
K
K
Klempnauer
K H
KH
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D009857:Oncogenes; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012326:RNA Splicing; D012333:RNA, Messenger / Q000032:analysis
D018840:HSP70 Heat-Shock Proteins; D012333:RNA, Messenger