This paper reports human mitochondrial DNA variability in West New Guinea (the least known, western side of the island of New Guinea), not yet described from a molecular perspective. The study was carried out on 202 subjects from 12 ethnic groups, belonging to six different Papuan language families, representative of both mountain and coastal plain areas. Mitochondrial DNA hypervariable region 1 (HVS 1) and the presence of the 9-bp deletion (intergenic region COII-tRNA(Lys)) were investigated. HVS 1 sequencing identified 73 polymorphic sites defining 89 haplotypes; the 9-bp deletion, which is considered a marker of Austronesian migration in the Pacific, was found to be absent in the whole West New Guinea study sample. Statistical analysis applied to the resulting haplotypes reveal high heterogeneity and an intersecting distribution of genetic variability in these populations, despite their cultural and geographic diversity. The results of subsequent phylogenetic approaches subdivide mtDNA diversity in West New Guinea into three main clusters (groups I-III), defined by sets of polymorphisms which are also shared by some individuals from Papua New Guinea. Comparisons with worldwide HVS 1 sequences stored in the MitBASE database show the absence of these patterns outside Oceania and a few Indonesian subjects, who also lack the 9-bp deletion. This finding, which is consistent with the effects of genetic drift and prolonged isolation of West New Guinea populations, lead us to regard these patterns as New Guinea population markers, which may harbor the genetic memory of the earliest human migrations to the island.
The experiments here reported demonstrate that the main non-coding region of rat mitochondrial DNA is symmetrically transcribed. We have identified stable heavy and light transcripts, whose pattern is rather complex, in the D-loop region of rat mitochondrial DNA. Their relative concentrations have been determined. We detected heavy transcripts which encompass the whole D-loop and more abundant heavy RNA species which we interpreted as transcripts terminating downstream of the 3' end of the last coded gene (Thr-tRNA). The processed heavy RNA species contain polyA, suggesting a strict association between cleavage and polyadenylation. The pattern of light transcripts shows a long RNA, which, starting from the light strand promoter, covers the whole segment, and shorter RNA species which seems to be actively processed at the level of the conserved sequence boxes, probably acting as primers. The symmetric transcription of the D-loop containing region of rat mitochondrial DNA, and in particular the presence of stable transcripts complementary to the putative RNA primers, suggest that mechanisms mediated by interaction between complementary transcripts (antisense RNAs) might play a role in the regulation of mitochondrial DNA replication and expression.
We have identified new transcripts in the region surrounding the L-strand replication origin (Ori L) of rat liver mitoehondrial DNA. In particular. we have detected previously unidentified intermediates of RNA processing on both the heavy and the light strands, such as precursors ol'the ND2 mRNA plus the Trp-tRNA and precursors of the tRNAs clustered in the Ori L region. This indicates that the mechanism of RNA processing in mitoehondria proceeds step-wise producing a variety of precursors of the instate forms. The other striking finding is the detection of antisense RNA species in the region of L-strand replication. Since a variety ofantisense transcripts were also found in the D-loop region of rat mitochondrial DNA, we suggest that they Hight play a regulatory role in the replication and expression ~f the mitochondrial genome.
bstract We have characterized the transcriptional pattern of the rat mitochondrial ND6containing region in vivo. We have identified a stable nyadenylated RNA species complementary for the full length of the ND6 mRNA. The analysis of the ND5 region has revealed the presence of I antisense RNA only at its 3' end. The presence of these stable antisense species complementary to structural genes is intriguing and suggests a rssible regulatory function. The quantitative analyses have demonstrated that the H transcripts, both codogenic and non-codogenic, are more stable an the L transcriptswe have defined the 5' end of the ND6 mRNA at the level of the ATG downstream of the tRNAo'". The mapping of the ND1 end has demonstrated that GTG is the first codon of the mRNA. Our findings suggest that the post-transcriptional mechanisms involved in the pression of the mt genome are much more numerous and complex than those already described in the literature.
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