Analysis of the Non-Coding Region of the Human Factor VIII Gene in Comparison with Selected Regions of the Intron 1 of Human Factor IX

To identify possible regulatory elements in the intronic regions of human coagulation factor VIII (hFVIII) gene, the non-coding sequences of this gene were compared to a selected parts of human factor IX (hFIX) intron-1 sequences whose regulatory functions had been suggested previously. With this aim, seven overlapping fragments of hFIX intron-1 were separately compared to the whole sequences taken from 25 introns of hFVIII gene. This comparative study has resulted in detection of several repeated sequences within hFVIII intronic regions, varying in size from 50 to 350 base pairs that are homologues to that of the hFIX-derived sequences. The detected elements show more than 74% homology to that of the sequences taken from hFIX gene. Although it is not possible to show a direct correlation between the numbers of repeated elements found in each intron and the intron length. However it seems that the distribution pattern and the number of repeated elements among hFVIII introns and within each intron are not random. In other word, the results show that the numbers of repeats in the first and last introns in the gene are higher than those of other internal introns. Reverse direction of a number neighboring elements in some of the introns may lead to the formation of stem-loop structures that might be effective in the stability of the hFVIII mRNA precursor. A survey within the 5'- and 3'-untranslated regions of the hFVIII gene detected a common sequence which is repeated in each region. Comparison of the repeated elements to the major repeated elements in human genome shows that the detected elements belong to sub-families of retrotransposon-derived elements, known as Alu sequences. Further sequence analysis of the repeated elements indicates in the presence of many short sequences with the potential of transcription-factor binding activity that supports the regulatory function of the repeated elemnts found in the hFVIII intronic regions. Experimental analysis of the detected sequences to examine their potential regulatory function on a candidate reporter gene is the next step to this work.