Novel human genes falling within the category of family genes relating to p53 gene which is known as a cell proliferation regulatory gene, and gene products thereof. A human p51 gene characterized by containing a base sequence encoding an amino acid sequence represented by SEQ ID NO:1; a human p51 gene having a base sequence consisting of the 145- to 1488-bases in the sequence represented by SEQ ID NO:2; vectors containing these genes; host cells transformed with these vectors; a process for producing a p51 protein having the amino sequence represented by SEQ ID NO:1; which comprises culturing the above host cells and harvesting the protein from the thus obtained culture; and the p51 protein having the amino acid sequence represented by SEQ ID NO:1.