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Two new members of the maf oncogene family, mafK and mafF, encode nuclear b-Zip proteins lacking putative
K T Fujiwara1, K Kataoka, M Nishizawa
1Department of Viral Oncology, Cancer Institute, Tokyo, Japan.
Abstract:
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 under moderately stringent hybridization conditions, we picked up a series of cDNA clones for a novel maf-related gene which we named mafK. We also identified another maf-related gene named mafF by screening a chicken genomic library using a mafK probe. Structural analyses suggested that the mafK and mafF genes consist of three exons. The exon-intron structures of the two genes resemble each other, but differ from that of the chicken c-maf gene. As compared to the c-Maf protein, the proteins 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 the b-Zip domain are well conserved among these Maf-related proteins. When overexpressed by using an avian retroviral vector, the two maf-related genes did not induce morphological transformation of CEF cells but induced colony formation in soft agar with very low efficiencies. With 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 different from one another, probably reflecting their different functions in vivo.
Insights
Researchers identified two novel maf-related genes, mafK and mafF, in chickens. These genes encode smaller proteins than c-Maf but share a conserved b-Zip domain, suggesting distinct cellular functions.
Area of Science:
- Molecular Biology
- Oncogenes
- Gene Expression
Background:
- The avian musculoaponeurotic fibrosarcoma virus oncogene v-maf encodes a nuclear protein with a b-Zip domain.
- Maf proteins are transcription factors characterized by a basic region leucine zipper (b-Zip) domain.
Purpose of the Study:
- To identify novel maf-related genes in chicken.
- To characterize the structure and function of newly identified maf genes.
Main Methods:
- Screening of chicken embryo fibroblast (CEF) cDNA library and chicken genomic library.
- Hybridization techniques and structural analysis of gene sequences.
- Overexpression studies using avian retroviral vectors and soft agar colony formation assays.
- Immunodetection of MafK protein in cell nuclei.
Main Results:
- Two novel maf-related genes, mafK and mafF, were identified.
- mafK and mafF genes have similar exon-intron structures, distinct from c-maf.
- The encoded MafK and MafF proteins are smaller than c-Maf, lacking the N-terminal acidic domain but retaining the b-Zip domain.
- Overexpression of mafK and mafF did not induce cell transformation but showed low-efficiency soft agar colony formation.
- MafK protein localizes predominantly to the nucleus.
- Expression patterns of mafK, mafF, and c-maf genes differ across tissues.
Conclusions:
- The novel mafK and mafF genes represent new members of the maf gene family in chickens.
- Structural differences suggest distinct functional roles compared to c-Maf.
- The nuclear localization and altered transformation potential of MafK and MafF indicate unique biological activities.