CLONING AND SEQUENCE-ANALYSIS OF THE GENE AND CDNA-ENCODING MOUSE SPERMIDINE SPERMINE N(1)-ACETYLTRANSFERASE - A GENE UNIQUELY REGULATED BYPOLYAMINES AND THEIR ANALOGS

The polyamine catabolizing enzyme, spermidine/spermine N1-acetyltransf erase (SSAT), has been implicated as a critical determinant of polyami ne pool maintenance. SSAT has recently been shown to be positively reg ulated in human cell lines by polyamines and their analogs at the leve l of mRNA accumulation. Mouse LA-4 lung adenoma cells treated with eit her spermine or the spermine analog, N1,N12-bis(ethyl)spermine, produc ed a 2.3 and 6.5-fold increase, respectively, in SSAT mRNA. Prior evid ence for transcriptional control of the enzyme prompted investigation of SSAT gene structure and its regulatory elements. The mouse SSAT gen e was isolated as a 3650 bp EcoRI fragment from a lambda-J1 Mus saxico la genomic library by hybridization with human SSAT cDNA. An additiona l 431 bp downstream from the 3' EcoRI site were sequenced from a BamHI fragment (total gene sequence, 4066 bp). The gene contains six exons and five introns. Sequence analysis of the 774 bp of the 5' non-coding region revealed the absence of TATAA or CCAAT sequence motifs and the presence of a number of binding motifs in the 5' region of the gene w ith consensus binding sequences for transcription factors SP1, AP1, E2 F, AP2, PEA-3 and others. The deduced amino acid sequence of the codin g region differs from that of the human SSAT cDNA by five amino acids. The 527 bp of the 3' non-coding region contains four possible polyade nylation signal sites of which only one displays a typical consensus s equence. A 940 bp SSAT cDNA was isolated from Mus domesticus (BALB-C) liver lambdagt11 cDNA library. It contains a 5' untranslated region 89 bp in length and a 3' untranslated region 376 bp in length. The amino acid sequence deduced from Mus domesticus differs from that of Mus sa xicola by one amino acid, from the hamster cDNA, by four amino acids a nd from the human cDNA by six amino acids. Further elucidation of the structural features of the SSAT gene may reveal how it is positively r egulated by polyamines and their analogs.