Polymorphism and mapping of the IGF1 gene,and absence of association with stature among African Pygmies

Summary Probes detecting restriction fragment length polymorphisms (RFLPs) in the insulinlike growth factor (IGF1) gene were isolated and allele frequencies in different human populations determined. No difference was detected between the distribution of IGF1 alleles in Pygmies versus non-Pygmy black Africans, despite the proposal that a defect in the IGF1 gene might be responsible for Pygmy short stature. This was supported by the absence of a correlation of IGF1 genotype with height in the C.A.R. Pygmies. Polymerase chain reaction (PCR) and direct sequencing failed to demonstrate an alteration in the region upstream the IGF1 start site in Pygmies. Linkage analysis demonstrated that IGF1 is tightly linked to the phenylalanine hydroxylase gene on chromosome 12q22–24.1.     

Salt tolerant sugarbeet progeny from tissue cultures challenged with multiple salts

Lines of sugarbeet (Beta vulgaris L.) tolerant of multiple salts was accomplished by an in vitro multiple salt challenge. Petioles were placed on RV medium amended with 5 different salts along with Murashige and Skoog base salts for one month. Surviving shoots were cultured on RV medium to obtain petioles for subsequent challenges. During the first, second and third challenges, organogenically regenerated shoots developed from 5%, 46%, and 80% of the petioles, respectively. After the third multiple salt challenge, tolerant shoots were rooted and transplanted in soil. Salt was added to this soil at 1.0% by weight and plants were observed for 2 months. The ten most salt tolerant plants were vernalized to obtain seed. The R₁ seed and controls were planted in soil containing 0%, 0.61% or 0.77% multiple salts per dry soil weight. Emergence of R₁ seedlings was significantly greater than the controls under salt stress. Multiple salt tolerant R₁ plants were maintained in salt amended soil to the 8–10 leaf stage and appeared as healthy and vigorous as the control growing in salt free soil.Contribution from Missouri Agricultural Experiment Station Journal Series No. 10948. University of Missouri, Columbia, MO, USA Mention of trade names does not constitute a guarantee or warranty of the product by University of Missouri of Holly Sugar Corporation and does not imply their approval to the exclusion of other products.     

Identification of 3-hydroxypalmitic acid methyl ester as a novel autoregulator controlling virulence in Ralstonia solanacearum

Expression of virulence genes in Ralstonia solanacearum , a phytopathogenic bacterium, is controlled by a complex regulatory network that integrates multiple signal inputs. Production of several virulence determinants is co-ordinately reduced by inactivation of phcB , but is restored by growth in the presence of a volatile extracellular factor (VEF) produced by wild-type strains of R. solanacearum . The VEF was purified from spent culture broth by distillation, solvent extraction, and liquid chromatography. Gas chromatography and mass spectroscopy identified 3-hydroxypalmitic acid methyl ester (3-OH PAME) as the major component in the single peak of VEF activity. Authentic 3-OH PAME and the purified VEF were active at ≤1 nM, and had nearly equivalent specific activities for stimulating the expression of eps (the biosynthetic locus for extracellular polysaccharide) in a phcB mutant. Authentic 3-OH PAME also increased the production of three virulence factors by a phcB mutant over 20-fold to wild-type levels, restored normal cell density-associated expression of eps and increased expression of eps when delivered via the vapour phase. Reanalysis of the PhcB amino acid sequence suggested that it is a small-molecule S -adenosylmethionine-dependent methyltransferase, which might catalyse synthesis of 3-OH PAME from a naturally occurring fatty acid. Biologically active concentrations of extracellular 3-OH PAME were detected before the onset of eps expression, suggesting that it is an intercellular signal that autoregulates virulence gene expression in wild-type R. solanacearum . Other than acyl-homoserine lactones, 3-OH PAME is the only endogenous fatty acid derivative shown to be an autoregulator and may be the first example of a new family of compounds that can mediate long-distance intercellular communication.     

Biochemical synthesis of chirally pure Rp oligonucleotide phosphorothioates

Oligonucleotide phosphorothioates have been synthesized using procaryotic DNA polymerase and oligonucleotide template/primer. The method facilitates the recovery of DNA polymerase and template/primer and is successful at the milligram scale. This revised version was published online in November 2006 with corrections to the Cover Date.     

Nicking by transesterification: the reaction catalysed by a relaxase

DNA relaxases play an essential role in the initiation and termination of conjugative DNA transfer. Purification and characterization of relaxases from several plasmids has revealed the reaction mechanism: relaxases nick duplex DNA in a site- and strand-specific manner by catalysing a transesterification. The product of the reaction is a nicked double-stranded DNA molecule with a sequestered 3'-OH and the relaxase covalently bound to the 5' end of the cleaved strand via a phosphotyrosyl linkage. The relaxase-catalysed transesterification is isoenergetic and reversible; a second transesterification ligates the nicked DNA. However, the covalent nucleoprotein complex is relatively long-lived, a property that is likely to be essential for its role as an intermediate in the process of conjugative DNA transfer. Subsequent unwinding of the nicked DNA intermediate is required to produce the single strand of DNA transferred to the recipient cell. This reaction is catalysed by a DNA helicase, an activity intrinsic to the relaxase protein in some, but not all, plasmid systems. The first relaxase-catalysed transesterification is essential for initiation of conjugative strand transfer, whereas the second is presumably required for termination of the process. The relaxase, in conjunction with several auxiliary proteins, forms the relaxation complex or relaxosome first described nearly 30 years ago as being associated with conjugative and mobilizable plasmids.     

Mitochondrial and nuclear genes present conflicting portraits of human origins

Human mitochondrial DNA (mtDNA) sequences reveal an abundance of polymorphic sites in which the frequencies of the segregating bases are very different. A typical polymorphism involves one base at low frequency and the other base at high frequency. In contrast, nuclear gene data sets tend to show an excess of polymorphisms in which both segregating bases are at intermediate frequencies. A new statistical test of this difference finds significant differences between mtDNA and nuclear gene data sets reported in the literature. However, differences in the polymorphism patterns could be caused by different sample origins for the different data sets. To examine the mtDNA-nuclear difference more closely, DNA sequences were generated from a portion of the X-linked pyruvate dehydrogenase E1 alpha subunit (PDHA1) locus and from a portion of mitochondrial control region I (CRI) from each of eight individuals, four from sub-Saharan Africa. The two genes revealed a significant difference in the site frequency distribution of polymorphic sites. PDHA1 revealed an excess of intermediate-frequency polymorphisms, while CRI showed an excess of sites with the low-high frequency pattern. The discrepancy suggests that mitochondrial variation has been shaped by natural selection, and may not be ideal for some questions on human origins.