MOLECULAR CHARACTERIZATION OF DUARTE-1 AND DUARTE-2 VARIANTS OF GALACTOSE-1-PHOSPHATE URIDYLTRANSFERASE

The N314D polymorphism was found in two different alleles of the galac tose-1-phosphate uridyltransferase (GALT) gene, Duarte-1 (D1) and Duar te-2 (D2). Although bath variants have identical electrophoretic mobil ity and isoelectrofocusing points, the galactose-1-phosphate uridyltra nsferase (GALT) activity varies: D1 aIleles showed 110-130% of the nor mal RBC activity, but D2 alleles only 40-50%. We found that D1 alleles also carried a silent mutation in exon 7 (L218L) in addition to N314D . In contrast, besides N314D, D2 alleles carried two regulatory mutati ons, G1105C and G1391A, in introns D and E, respectively. In normal an d Q188R alleles none of the above four mutations coexisted, However, s ome galactosaemia alleles with mutations other than Q 188R, such as W3 16X and E340X of exon 10, also carried the N314D mutation. The W316X aIleles existed in cis with the intron mutations (G1105C and G1391A), whereas those with E340X are in cis with L218L. In all cases examined, the intron mutations were not found in D1 alleles and no D2 alleles h ad the silent mutation of L218L. These results suggest that the decrea se in the GALT activity in D2 may be due to regulation of the GALT gen e expression. The G1105C site may be critical to the function of eryth roid transcription factor NF-E1, since it flanks the core consensus se quence for one of its binding sites. The G1391A mutation may affect an other cia-acting regulatory sequence. Alternatively, both mutations ma y be involved in an aberrant splice processing, which possibly results in a low level of correctly spliced mRNA.