Mol Cell Biol, February 1998, p. 989-1002, Vol. 18, No. 2
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Hanson Centre for Cancer Research, Institute of Medical and Veterinary Science, Adelaide, South Australia 5000,1 and Joint Protein Structure Laboratory of the Ludwig Institute for Cancer Research and Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052,2 Australia; Laboratory of Molecular Genetics, Tsukuba Life Science Center, The Institute of Physical and Chemical Research (RIKEN), Tsukuba, Ibaraki 305, Japan3; and Mammalian Genetics Laboratory, ABL-Basic Research Program, National Cancer Institute-Frederick Cancer Research and Development Center, Frederick, Maryland 217024
Received 15 September 1997/Accepted 11 November 1997
We have previously detected two related murine nuclear proteins, p160 and p67, that can bind to the leucine zipper motif within the negative regulatory domain of the Myb transcription factor. We now describe the molecular cloning of cDNA corresponding to murine p160. The P160 gene is located on mouse chromosome 11, and related sequences are found on chromosomes 1 and 12. The predicted p160 protein is novel, and in agreement with previous studies, we find that the corresponding 4.5-kb mRNA is ubiquitously expressed. We showed that p67 is an N-terminal fragment of p160 which is generated by proteolytic cleavage in certain cell types. The protein encoded by the cloned p160 cDNA and an engineered protein (p67*) comprising the amino-terminal region of p160 exhibit binding specificities for the Myb and Jun leucine zipper regions identical to those of endogenous p160 and p67, respectively. This implies that the Myb-binding site of p160 lies within the N-terminal 580 residues and that the Jun-binding site is C-terminal to this position. Moreover, we show that p67* but not p160 can inhibit transactivation by Myb. Unexpectedly, immunofluorescence studies show that p160 is localized predominantly in the nucleolus. The implications of these results for possible functions of p160 are discussed.
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