A dimorphic Alu Sb-like insertion in COL3A1 is ethnic-specific

Alu elements are a class of repetitive DNA sequences found throughout the human genome that are thought to be duplicated via an RNA intermediate in a process termed retroposition. Recently inserted Alu elements are closely related, suggesting that they are derived from a single source gene or closely related source genes. Analysis of the type III collagen gene (COL3A1) revealed a polymorphic Alu insertion in intron 8 of the gene. The Alu insertion in the COL3A1 gene had a high degree of nucleotide identity to the Sb family of Alu elements, a family of older Alu elements. The Alu sequence was less similar to the consensus sequence for the PV or Sb2 subfamilies, subfamilies of recently inserted Alu elements. These data support the observations that at least three source genes are active in the human genome, one of which is distinct from the PV and Sb2 subfamilies and predates either of these two subfamilies. Appearance of the Alu insertion in different ethnic populations suggests that the insertion may have occurred in the last 100,000 years. This Alu insert should be a useful marker for population studies and for marking COL3A1 alleles.     

A new method of bipolymerase sequencing prevents “stop-bands”

This article presents a relatively quick and cost-effective DNA sequencing method that prevents the formation of stop-bands. This method uses a combination ofTaq and Sequenase that allows sequencing at both low and high temperatures. The ability to sequence at a high temperature appears to be the fundamental component in preventing stop-band formation in G + C rich regions.     

Development and germination of pecan somatic embryos derived from liquid culture

Aggregates of globular and pre-globular stage somatic embryos from suspension cultures of pecan (Carya illinoensis Koch) were cultured on solidified media for embryo development. Embryo aggregates and pre-globular stage embryo masses were given various treatments to further ontologic development. A 2- to 4-wk mild dehydration of the embryo aggregates suppressed recurrent embryogenesis, promoted development of globular embryos into cotyledonary stage embryos, and enhanced plant development beyond germination. Fine embryogenic tissue masses filtered from suspension formed cotyledonary-staged embryos when the collection filters were plated on solified medium. The embryogenic capacity of preglobular stage embryo masses was compared between media supplemented with varying concentrations of polyethylene glycol (molecular weight 8 000) vs. filter overlays. The filter paper overlays were not necessary for embryo development. An inverse relationship was found between the number of embryos that developed and the concentration of polyethylene glycol in the medium. However, this relationship was reversed for ability of embryos to germinate and develop into a plant.     

The homologous operons for P1 and P7 plasmid partition are autoregulated from dissimilar operator sites

The plasmid-partition regions of the P1 and P7 plasmid prophages in Escherichia coli are homologues which each encode two partition proteins, ParA and ParB. The equivalent PI and P7 proteins are closely related. In each case, the proteins are encoded by an operon that is autoregulated by the ParA and ParB proteins in concert. This regulation is species-specific, as the P1 proteins are unable to repress the P7 par operon and vice versa. The homologous ParA proteins are primarily responsible for repression and bind to regions that overlap the operon promoter in both cases. The DNA-binding domain of the P7 auto-repressor lies in the amino-terminal end of the P7 ParA protein. This region includes a helix-turn-helix motif that has a clear counterpart in the P1 ParA sequence. However, despite the common regulatory mechanism and the similarity of the proteins involved in repression, the promoter-operator sequences of these two operons are very different in sequence and organization. The operator is located downstream of the promoter in P1 and upstream of it in P7, and the two regions show little, if any, homology. How these differences may have arisen from a common ancestral form is discussed.     

Influence of photoperiod and medium formulation on peanut somatic embryogenesis

Somatic embryos were produced from peanut (Arachis hypogaea L.) immature zygotic cotyledons. Comparisons were made of the level of -naphthaleneacetic acid during induction, nitrogen formulation of the medium, and photoperiod. Over 70% embryogenesis was obtained regardless of NAA level used. Percent embryogenesis and number of embryos were markedly lower in explants induced on NAA compared to 2,4-D. Embryo production was not greatly affected by either the use of Murashige & Skoog versus Finer & Nagasawa salts or light versus dark culture conditions. However, embryo morphology was noticeably affected by photoperiod. Embryos produced under a 16 h photoperiod were tough, woody and difficult to separate for subsequent germination and conversion. Those produced under a 0-h photoperiod were succulent and pliable.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - NAA -naphthaleneacetic acid - MS Murashige & Skoog (1962) - B5 Gamborg et al. (1968) - picloram 4-amino-3,5,6-trichloropicolinic acid - FN Finer & Nagasawa (1988) - 2,4,5-T 2,4,5-trichlorophenoxyacetic acid     

The role of tyrosine-114 in the enzymatic activity of the Shiga-like toxin I A-chain

Shiga-like toxin I (SLT-I), the potent cytotoxin produced by certain pathogenic strains of Escherichia coli, is a member of a burgeoning family of ribosome-inactivating proteins (RIPS), which share common structural and mechanistic features. The prototype of the group is the plant toxin ricin. Recently we proposed a structural model for the Slt-IA active site, based in part on the known geometry of the enzymatic subunit of the ricin toxin. The model places three aromatic residues within the putative Slt-IA active site cleft: tyrosine 77, tyrosine 114, and tryptophan 203. Here we present biochemical and biophysical data regarding, the phenotypes of conservative point mutants of Slt-IA in which tyrosine 114 is altered. We used oligonucleotide-directed mutagenesis to replace tyrosine 114 with either phenylalanine (Y114F) or serine (Y114S). Periplasmic extracts of E. coli containing wild-type or mutant Slt-IA were tested for their ability to inhibit protein synthesis in vitro. Relative to wild-type, the activity of mutant Y1 14F was attenuated about 30-fold, while the mutant Y114S was attenuated about 500 to 1000-fold. In order to address the possibility that differential activation of the mutants rather than local effects at the active site might account for their diminished activity, we engineered the same mutations into a truncated slt-IA cassette that directs expression of a product corresponding to the activated A₁ form of Slt-IA (wild-type-). The same general relationships held: relative to wild type-, Y114F- was attenuated about 7-fold, and Y114S- about 300-fold. Tryptic digestion profiles of the mutant proteins were similar to those of the corresponding wild-type, indicating that the amino acid substitutions had not caused major alterations in conformation. We conclude that Y114 plays a significant role in the activity of Slt-IA, one which is quantitatively similar to that of Y77, and one which is predicated on the presence of both its weakly acidic phenolic hydroxyl and its aromatic ring.     

MUSOPSIS N. GEN.: A BANANA-LIKE LEAF GENUS FROM THE EARLY TERTIARY OF EASTERN NORTH GREENLAND

A fossil flora from the Late Paleocene-Early Eocene Thyra Ø Formation of eastern North Greenland (paleolatitude 77° N) has yielded monocotyledon leaf impressions with characters seen only in the closely related modem species in the families of Heliconiaceae, Musaceae, and Strelitziaceae. The combination of large costae widths and parallel, nonanastomosing, lateral veins that depart at right angles from the costae in the fossil material are features present only in leaves of extant species from these families. Three basic venation patterns also are recognized in the modem species of these families, but except for the genera Strelitzia and Phenakospermum, none of these patterns are present exclusively in any one family. Musopsis n. gen. is created for the fossil material from Greenland, but it is considered a form genus due to the lack of gross morphological features that can be used for separating leaves of the modem genera in Heliconiaceae, Musaceae, and Strelitiziaceae. It is the first known Arctic occurrence of fossil leaf material resembling this modem group of taxa.