Genomic organization of a tumor growth inhibitor gene ING1

ING1, a supposed tumor suppressor gene, codes for a p33 protein involved in cell proliferation control and regulation of apoptosis. A GenBank search r evealed two groups of expressed sequence tags corresponding to ING1 mRNA fo rms. The 3' exon 2 is the same in both forms whereas the 5' exons la and Ib differ. ING1-containing cosmids were found in the LA13NC05 library. Each I NG1 exon and flanking introns were sequenced using the cosmid 80H9 template . In the genome, the exons are arranged as 1b-1a-2. RT-PCR showed that both mRNA forms are simultaneously present in cell lines. The deduced amino aci d sequence for 1b-2 proved similar to those of human proteins ING1L (2e(-72 )) and ING1L-7 (6e(-24)) and several proteins of lower eukaryotes having th e ING-specific N-terminal domain and the zinc-binding domain PHD. Hence the ING-like proteins can be regarded as a separate evolutionarily old family. A peculiarity of the ING1 structure is the CpG islands surrounding each of its three exons, suggesting regulation of its expression through de novo m ethylation. The data on the fine structure of ING1 and its mRNA forms permi t mutation screening and assessment of its methylation status in human tumo r specimens.