Kt. Fujiwara et al., 2 NEW MEMBERS OF THE MAF ONCOGENE FAMILY, MAFK AND MAFF, ENCODE NUCLEAR B-ZIP PROTEINS LACKING PUTATIVE TRANSACTIVATOR DOMAIN, Oncogene, 8(9), 1993, pp. 2371-2380
The v-maf oncogene of the avian musculoaponeurotic fibrosarcoma virus,
AS42, encodes a nuclear protein which contains a characteristic b-Zip
domain. By screening a chicken embryo fibroblast (CEF) cDNA library u
nder moderately stringent hybridization conditions, we picked up a ser
ies of cDNA clones for a novel maf-related gene which we named mafK. W
e also identified another maf-related gene named mafF by screening a c
hicken genomic library using a mafK probe. Structural analyses suggest
ed that the mafK and mafF genes consist of three exons. The exon-intro
n structures of the two genes resemble each other, but differ from tha
t of the chicken c-maf gene. As compared to the c-Maf protein, the pro
teins encoded by the mafK and the mafF genes are rather small in size
and lack the regions corresponding to the amino terminal acidic domain
present in the c-Maf protein. On the other hand, the structures of th
e b-Zip domain are well conserved among these Maf-related proteins. Wh
en overexpressed by using an avian retroviral vector, the two maf-rela
ted genes did not induce morphological transformation of CEF cells but
induced colony formation in soft agar with very low efficiencies. Wit
h a specific antibody, the MafK protein was detected predominantly in
the nuclei of the cells infected with the virus which carries the mafK
gene. Tissue distributions of these three maf-family genes are differ
ent from one another, probably reflecting their different functions in
vivo.