当前位置： SCI文献检索 > HEREDITY期刊下所有文献 > Evolution of the rDNA spacer, ITS 2, in the ticks Ixodes scapularis and I. pacificus (Acari: Ixodidae).

Evolution of the rDNA spacer, ITS 2, in the ticks Ixodes scapularis and I. pacificus (Acari: Ixodidae).

Abstract：

:Evolution of the rDNA spacer, ITS 2, is examined by comparing 17 DNA sequences of the ticks, Ixodes scapularis and I. pacificus. The distribution of fixed interspecific differences and the relative frequency of base changes vs. insertions/deletions (indels) matches the distribution and relative frequency for intraspecifically variable sites. This suggests that most intraspecific variation is not effectively selected against. The base composition of the ITS 2 transcript is G- and U-biased. But, 5-base regions enriched (> 80 per cent) for A or U occur more frequently than expected while G- and C-enriched regions occur less frequently than expected. Enriched sequences may be prone to replication slippage, accounting for the A/T bias in insertions. Slippage-mediated gains and losses of A/T-rich tandem repeats apparently account for most indels. Minimum-energy conformations of the two species' folded transcripts share major structural features. Structural inertia arises from intramolecular base pairing within stems that allows most mutations to be absorbed as new bulges off stems. Yet, there is evidence of selection to maintain the conformation. First, intraspecifically variable sites are concentrated at the ends of stems in loops and intersections, structures that do not contribute to intramolecular base pairing. Moreover, some indels that have become fixed in one species compensate for the presence of conformation-destabilizing indels. However, high rates of sequence evolution within stems and absence of compensatory base evolution contraindicates selective constraint. Degenerate dispersed and tandem copies of two subrepeats, each approximately 20 bases long, may account for much of the ITS 2 sequence. These are approximately inverses of each other and are, consequently, capable of significant intramolecular hydrogen bonding to produce folded transcripts of low energy. Evolution of the ITS 2 sequence may largely entail replication slippage-mediated gains and losses of these repeats or their composite subrepeats.

journal_name

Heredity (Edinb)

journal_title

Heredity

authors

McLain DK,Wesson DM,Collins FH,Oliver JH Jr

doi

10.1038/hdy.1995.139

subject

Has Abstract

pub_date

1995-09-01 00:00:00

pages

303-19

eissn

0018-067X

issn

1365-2540

journal_volume

75 ( Pt 3)

pub_type

杂志文章

在线工具

Evolution of the rDNA spacer, ITS 2, in the ticks Ixodes scapularis and I. pacificus (Acari: Ixodidae).