Reference "Mitochondrial sequence migrated downstream to a nuclear V-ATPase B gene is transcribed but non-functional"

Reference ID

6538

Title

Mitochondrial sequence migrated downstream to a nuclear V-ATPase B gene is transcribed but non-functional

Source

Gene, 2001, vol. 271, pp. 193-201

Authors (4)

Kubo-N	Takano-M
Nishiguchi-M	Kadowaki-K

Abstract

A promiscuous nuclear sequence containing a mitochondrial DNA fragment was
isolated from rice. Nucleotide sequence analysis reveals that the cDNA clone #21
carries a mitochondrial sequence homologous to the 3' portion of the rps19 gene
followed by the 5' portion of the rps3 gene. The mitochondrial sequence is
present in an antisense orientation. Sequence comparison of the #21 cDNA with
the original mitochondrial sequence shows 99% similarity, suggesting a recent
transfer event. Moreover, evidence for a lack of an RNA editing event and
retaining of the group II intron sequence strongly suggests that the sequence
was transferred from mitochondrion to the nucleus via DNA rather than RNA as an
intermediate. The upstream region to the mitochondria-derived sequence shows
homology to part of the vacuolar H(+)-ATPase B subunit (V-ATPase B) gene.
Isolation of a functional V-ATPase B cDNA and its comparison with the #21 cDNA
reveal a number of nucleotide substitutions resulting in many translational stop
codons in the #21 cDNA. This indicates that the #21 cDNA sequence is not
functional. Analysis of genomic sequences shows the presence of five intron
sequences in the #21 cDNA, whereas the functional V-ATPase B gene has 14
introns. Of these, three exons and their internal two introns are homologous to
each other, suggesting a duplication event of V-ATPase B genomic DNA. The
results of this investigation strongly suggest that the mitochondrial sequence
was integrated in an antisense orientation into the pre-existing V-ATPase B
pseudogene that can be transcribed and spliced. This represents a case of
unsuccessful gene transfer from mitochondrion to the nucleus.