Distribution of the mammalian-wide interspersed repeats (MIRs) in the isochores of the human genome

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The distribution of MIRs (mammalian-wide interspersed repeats) was investigated in 164 human sequences (≥100 kb), which were assigned, according to their GC level, to isochore families L, H1, H2 and H3. MIR elements, whose total number in the genome was estimated to be about 3.3×10 5, were found to be unevenly distributed in human isochores. The majority of MIRs (55%) were found in the L isochore family. In contrast, MIR density was highest in H2, closely followed by H1, whereas densities in L and H3 were 2- and 3-fold lower than in H2, respectively. For this reason, the assessment of MIR distribution by inter-repeat PCR led to an overestimation of MIR numbers in H2 isochore and an underestimation in L isochores.