Organization of 5S-Histone Genes in Different Artemia Populations
We have been studying 5S rRNA genes in different populations of Artemia. We have found in all cases that 5S genes are linked to histone genes. In all of the populations studied, there are two types of 5S-histone genes, differing both in size and restriction map. According to the organization of these genes, the populations we have studied can be grouped into three categories: bisexuals from North America, bisexuals from Eurasia and parthenogenetic populations from Eurasia.
We have studied in detail three recombinant clones that hybridize with 5S rRNA, one from a North American bisexual and the other two from a Chinese parthenogenetic population. Histone genes are clustered in 3.5 kb segments, separated by 500 bp from the 5S rRNA gene; one is of around 350 bp, including the spacer regions. The histone closest to the 5S gene is H2A. Comparison of the distribution of flanking sequences around the 5S gene, as well as the fact that the majority of 5S and histone genes are linked together suggest that 5S rRNA gene sequences invaded the histone repeat before amplification of this complex unit.
We are currently studying whether this organization of 5S-histone genes is of wider occurrence, or whether it is just a peculiarity of the genus Artemia.