CLONING, MAPPING, EXPRESSION, FUNCTION, AND MUTATION ANALYSES OF THE HUMAN ORTHOLOG OF THE HAMSTER PUTATIVE TUMOR-SUPPRESSOR GENE DOC-1

doc-1 is a putative tumor suppressor gene isolated and identified from the hamster oral cancer model, Here, we report the molecular cloning and the functional characterization of the human ortholog of the hamst er doc-l gene, Human doc-l cDNA is 1.6 kilobase pairs in length and en codes for a 115-amino acid polypeptide (12.4 kDa, pi 9.53). Sequence a nalysis showed 98% identity between human and hamster doc-l protein se quences. DOC-1 is expressed in all normal human tissues examined. In o ral keratinocytes, expression of DOC-1 is restricted to normal oral ke ratinocytes, By immunostaining of normal human mucosa, DOC-1 is detect ed in both the cytoplasm and nuclei of basal oral keratinocytes; while in suprabasilar cells, it is primarily found in the nuclei, Human ora l cancers in vivo did not exhibit immunostaining for DOC-1, Like murin e DOC-1, human DOC-1 associates with DNA polymerase alpha/primase and mediates the phosphorylation of the large p180 catalytic subunit, sugg esting it may be a potential regulator of DNA replication in the S pha se of the cell cycle, Using a human doc-l cosmid as a probe, human doc -l is mapped to chromosome 12q24. We identified four exons in the enti re human doc-l gene and determined the intron-exon boundaries. By poly merase chain reaction and direct sequencing, we examined premalignant oral lesion and oral cancer cell lines and found no intragenic mutatio ns.