RETARDED AND ABERRANT SPLICINGS CAUSED BY SINGLE EXON MUTATION IN A PHOSPHOGLYCERATE KINASE VARIANT

The molecular abnormality of a phosphoglycerate kinase variant which w as associated with severe tissue enzyme deficiency and episodes of mus cle contractions and myoglobinuria was examined. Analysis of the patie nt's DNA showed the existence of a nucleotide transversion AIT --> C/G in exon 7. No other nucleotide change was detected, in the coding reg ion of the variant gene. The mutation should produce a single amino ac id substitution Glu --> Ala at protein position 251 counting from the NH2-terminal acetyl serine residue. The protein abnormality caused by the amino acid substitution cannot explain the enzyme deficiency. Nort hern blot hybridization indicated that the PGK mRNA content of the pat ient's lymphoblastoid cells was only about 10% of that of normal. Nucl eotide sequence analysis revealed the existence of two PGK mRNA compon ents in the patient's cells. The major component corresponds to the no rmal PGK mRNA except for A --> C change at nucleotide position 755 cou nting from adenine of the chain initiation codon. The minor component contains 5' region (52 bases) of intron 7 between exon 7 and exon 8, A n inframe chain termination codon exists in the minor mRNA component, and the COOH-terminal half is expected to be deleted in the translatio n product. These results indicate that the low PGK activity in the pat ient's tissues is mainly due to retarded and aberrant pre-mRNA splicin gs caused by the change of the consensus 5' splice sequence AGgt to a nonconsensus sequence CGgt at the junction between exon 7 and intron 7 of the variant gene. (C) 1996 Academic Press, Inc.