Sequence conservation in kringle IV-type 2 repeats of the LPA gene

We have studied the homology of repeating kringle IV-type 2 (K IV-type 2) e lements of the LPA gene. Two K IV-type 2 genomic polymerase chain reaction (PCR) fragment libraries were constructed, one from an individual with high and one from an individual with low Lp(a) lipoprotein level, Only minor K IV-type 2 repeat length heterogeneity was observed. Sequence analysis data from the cloned K IV-type 2 repeats revealed a high degree of LPA sequence conservation in exons as well as in introns both within and between the two libraries. This sequence conservation of the IV-type 2 kringles is in agre ement with our previously reported results of simultaneous 'batch' DNA sequ ence analyses of all the K IV-type 2 repeals from single individuals. Seque nce data from the clones, combined with genomic DNA sequencing, revealed th at the K IV-type 2 reading frame of exons 1 and 2 are extended into the con served flanking introns by 519 base pairs (bp) and 312 bp, respectively. Th e theoretical coding capacity of the exon 1 extended open reading frame (OR F I) is three times larger (173 amino acids, aa) than the translated exon 1 , and that of the extended open reading frame of exon 2 (ORF II) is about t wice (104 aa) the length of exon 2. A central portion of the intron separat ing exons 1 and 2 also exhibited a high degree of sequence conservation, wi th the exception of a polymorphic CA repeat. Within the 61 K IV repeat clon es analysed, 19 different CA repeat patterns with 12-18 CA dinucleotide rep eats were observed. A comparison between the 37 clones from the individual with high Lp(a) lipoprotein level and the 24 clones from the individual wit h low Lp(a) lipoprotein level, revealed that seven of the CA repeat variant s were present in both clone libraries. The observed high level of sequence conservation in K IV-type 2 exons and introns matches relevant areas of th e plasminogen gene, and our findings fit with recent. K IV-type 2 duplicati ons and evolutionary selection pressure theories, although gene conversion events could also explain the findings. DNA sequences within K IV-type 2 ap peared to have no influence on Lp(a) lipoprotein level. (C) 2000 Elsevier S cience Ireland Ltd. All rights reserved.