Different transcription activity of HERV-K LTR-containing and LTR-lacking genes of the KIAA1245/NBPF gene subfamily.

Long terminal repeats (LTRs) of human endogenous retroviruses (HERVs) located near or within genes might affect their expression. We used the KIAA1245/NBPF human gene subfamily in an attempt to assess the regulatory potential of HERV LTRs. The subfamily includes five closely related paralogous genes: three of them contain an LTR in the second intron, and two genes lack it. Earlier we reported that the second and third exons of only LTR-containing genes of this subfamily could be detected in mature mRNAs of various cell lines and human tissues. The corresponding parts of mRNA of LTR-lacking genes analyzed in our study were absent from EST libraries, but other fragments of their mRNAs were available in EST databases. For a more unbiased view on the correlation between gene transcription and the intronic LTRs, in the present work we analyzed non-spliced pre-mRNA thus avoiding splicing effects. Based on RT-PCR analysis, we demonstrated that the KIAA1245/NBPF LTR-lacking gene AL592309/NBPF3 was transcriptionally active, but the LTR-containing genes showed significantly higher transcription levels. The data are in agreement with the suggestion that HERV-K LTRs within the second intron of the KIAA1245/NBPF subfamily genes might affect their transcriptional activity. However, it still remains to be investigated whether the revealed effect is due just to the LTR insertion or other factors are responsible for the difference.