Røsby O, Aleström P, Berg K
Institute of Medical Genetics, University of Oslo, POB 1036, 0315 Blindern, Oslo, Norway.
Atherosclerosis. 2000 Feb;148(2):353-64. doi: 10.1016/s0021-9150(99)00285-3.
We have studied the homology of repeating kringle IV-type 2 (K IV-type 2) elements 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 agreement with our previously reported results of simultaneous 'batch' DNA sequence analyses of all the K IV-type 2 repeats from single individuals. Sequence data from the clones, combined with genomic DNA sequencing, revealed that the K IV-type 2 reading frame of exons 1 and 2 are extended into the conserved flanking introns by 519 base pairs (bp) and 312 bp, respectively. The theoretical coding capacity of the exon 1 extended open reading frame (ORF 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 twice (104 aa) the length of exon 2. A central portion of the intron separating exons 1 and 2 also exhibited a high degree of sequence conservation, with the exception of a polymorphic CA repeat. Within the 61 K IV repeat clones analysed, 19 different CA repeat patterns with 12-18 CA dinucleotide repeats were observed. A comparison between the 37 clones from the individual with high Lp(a) lipoprotein level and the 24 clones from the individual with low Lp(a) lipoprotein level, revealed that seven of the CA repeat variants 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 the plasminogen gene, and our findings fit with recent K IV-type 2 duplications and evolutionary selection pressure theories, although gene conversion events could also explain the findings. DNA sequences within K IV-type 2 appeared to have no influence on Lp(a) lipoprotein level.
我们研究了LPA基因重复的kringle IV型2（K IV型2）元件的同源性。构建了两个K IV型2基因组聚合酶链反应（PCR）片段文库，一个来自Lp(a)脂蛋白水平高的个体，另一个来自Lp(a)脂蛋白水平低的个体。仅观察到K IV型2重复长度存在微小的异质性。来自克隆的K IV型2重复序列的序列分析数据显示，两个文库内部和之间的外显子以及内含子中LPA序列都具有高度保守性。IV型2kringle的这种序列保守性与我们先前报道的对单个个体所有K IV型2重复序列进行同步“批量”DNA序列分析的结果一致。来自克隆的序列数据与基因组DNA测序相结合，表明外显子1和2的K IV型2阅读框分别延伸到保守的侧翼内含子中519个碱基对（bp）和312 bp处。外显子1延伸的开放阅读框（ORF I）的理论编码能力比翻译后的外显子1大三倍（173个氨基酸，aa），外显子2延伸的开放阅读框（ORF II）的长度约为外显子2的两倍（104 aa）。分隔外显子1和2的内含子的中心部分也表现出高度的序列保守性，除了一个多态性的CA重复序列。在分析的61个K IV重复克隆中，观察到19种不同的CA重复模式，其中包含12 - 18个CA二核苷酸重复序列。对来自Lp(a)脂蛋白水平高的个体的37个克隆和来自Lp(a)脂蛋白水平低的个体的24个克隆进行比较，发现两个克隆文库中都存在7种CA重复变体。在K IV型2外显子和内含子中观察到的高度序列保守性与纤溶酶原基因的相关区域相匹配，我们的发现符合最近的K IV型2重复和进化选择压力理论，尽管基因转换事件也可以解释这些发现。K IV型2内的DNA序列似乎对Lp(a)脂蛋白水平没有影响。
