Genbank accession #: AJ131961

Plant Molecular Biology -     

Gene conversion and natural selection in the evolution of X-linked color vision genes in higher primates

During higher primate evolution, gene conversion seems to have occurred often between the red and green photo-pigment genes, which are tandemly linked on the X chromosome. To understand this phenomenon better, intron 4 sequences of the red and green pigment genes of a male human (an Asian Indian), a male chimpanzee, and a male baboon were amplified by PCR and sequenced. The data show that the intron 4 sequences between the two genes have been strongly or completely homogenized in the three species studied. Apparently recent gene conversion events have occurred in introns 4 of the red and green pigment genes in humans and chimpanzees. Two or more conversion events may have occurred at different times in introns 4 of the two pigment genes in baboons. The divergence between the two genes is significantly lower in intron 4 than in exons 4 and 5 in each species, contrary to the usual situation that introns evolve faster than exons. It is most likely that strong natural selection for maintaining the distinct functions of exons 4 and 5 of the red and green pigment genes has acted against sequence homogenization of these exons.      

Comparative genomics of chondrichthyan Hoxa clusters

Background  

The chondrichthyan or cartilaginous fish (chimeras, sharks, skates and rays) occupy an important phylogenetic position as the sister group to all other jawed vertebrates and as an early lineage to diverge from the vertebrate lineage following two whole genome duplication events in vertebrate evolution. There have been few comparative genomic analyses incorporating data from chondrichthyan fish and none comparing genomic information from within the group. We have sequenced the complete Hoxa cluster of the Little Skate (Leucoraja erinacea) and compared to the published Hoxa cluster of the Horn Shark (Heterodontus francisci) and to available data from the Elephant Shark (Callorhinchus milii) genome project.     

Immunochemical Investigations with Highly Purified Glutamate Dehydrogenase from Pea Seeds by Means of the Ouchterlony Test

Monospecific antibodies have been prepared with a homogeneousprotein fraction of the main activity band of pea seed glutamatedehydrogenase. This protein precipitates with its antibodiesin a single band with complete fusion as seen by the Ouchterlonydouble-diffusion test. Identical behaviour is observed withthe protein of the adjacent activity bands of the multiple molecularforms of this enzyme and the antibodies to the former fraction.Organ-specific ‘isoenzymes’ of glutamate dehydrogenasewith preparations of pea roots and epicotyls are not detectedby this procedure. Partially purified glutamate dehydrogenasepreparations from Lemna perpusilla, Zea mays, and Oryza sativaalso precipitate with the antibodies to the pea protein. TheLemna protein is shown to be different from the pea enzyme asjudged from immunological behaviour. The pea antibodies¹ donot cross-react with glutamate dehydrogenases from Candida orbeef liver, nor do the beef liver antibodies react with thepea and Candida enzymes.     

X-ray Microanalysis of the Mineral Contents of Some Protozoa

With the aid of energy-dispersive X-ray microanalysis, several protozoa were tested for content of cations within inorganic minerals. The skeleton of acantharia consists mainly of Sr with small quantities of Ca and Ba. Two Loxodes species contain nothing but Ba, while in some Remanella species Sr with small quantities of Ba were present. In one Geleia species, Ca with small quantities of Sr was found; in two Trachelocerca species from Sylt (Germany), Ba is there in addition. Another Trachelocerca species from northern Italy lacked Ba, but did possess Mn. In Prorodon only Ca was found.     

Estimating the age of the common ancestor of a sample of DNA sequences

We present a simple Monte Carlo method for estimating the age of the most recent common ancestor (MRCA) of a sample of DNA sequences. We show that Templeton's (1993) estimator of the age of the MRCA based on the maximum number of nucleotide differences between two sequences in a sample is inaccurate, and we demonstrate the new method by reanalyzing a sample of DNA sequences from human Y chromosomes and a sample of human Alu sequences.      

Order out of chaos in the nucleus

A report on the 'Nuclear architecture and control of gene expression' minisymposium at the first meeting of the European Life Scientists Organisation (ELSO), Geneva, Switzerland, September 2-6, 2000.     

Intronic gene conversion in the evolution of human X-linked color vision genes

Human red and green visual pigment genes are X-linked duplicate genes. To study their evolutionary history, introns 2 and 4 (1,987 and 1,552 bp, respectively) of human red and green pigment genes were sequenced. Surprisingly, we found that intron 4 sequences of these two genes are identical and that the intron 2 sequences differ by only 0.3%. The low divergences are unexpected because the duplication event producing the two genes is believed to have occurred before the separation of the human and Old World monkey (OWM) lineages. Indeed, the divergences in the two introns are significantly lower than both the synonymous divergence (3.2% +/- 1.1%) and the nonsynonymous divergence (2.0% +/- 0.5%) in the coding sequences (exons 1-6). A comparison of partial sequences of exons 4 and 5 of human and OWM red and green pigment genes supports the hypothesis that the gene duplication occurred before the human-OWM split. In conclusion, the high similarities in the two intron sequences might be due to very recent gene conversion, probably during evolution of the human lineage.