A rapid single-stranded cloning strategy for producing a sequential series of overlapping clones for use in DNA sequencing: application to sequencing the corn mitochondrial 18 S rDNA

A simple new procedure was described for producing a sequential series of overlapping clones for use in DNA sequencing. The technique used single-stranded M13 DNA and complementary DNA oligomers to form specific cleavage and ligation substrates. It was, therefore, independent of the sequence of the DNA cloned into the vector. Deletions of varying sizes were generated from one end of the insert through the 3' to 5' exonuclease activity of T4 DNA polymerase. The approximate size of the deletion and therefore the starting point for DNA sequencing could be estimated by electrophoresis of the subcloned phage DNA on a agarose gel. This greatly reduced the number of templates that must be sequenced to obtain a complete sequence. The entire procedure could be carried out in one tube in less than a day. The procedure was used to subclone and sequence the maize mitochondrial 18 S rDNA and 5' flanking region (2622 bases) in less than a week. Other applications of oligomers and single-stranded DNA in the construction of insertions, deletions, and cDNAs are discussed.     

Lineage analysis of the olfactory epithelium using a replication-incompetent retrovirus

We have analysed the lineage of olfactory receptor neurons usinga replication-incompetent retrovirus injected beneath the olfactoryepithelium of young rats. There are two major types of clustersof infected cells seen at 5–40 days after infection: (i)horizontal basal cells (HBCs); (ii) variable numbers of globosebasal cells (GBCs), and immature and mature sensory neurons.Olfactory nerve lesion increased the frequency of the globose/sensoryneuron clusters, as well as the number of cells/cluster, butdid not change the number of HBC clusters or cells/cluster.No clusters contained sustentacular cells. These data indicatethat, at least in young rats: (i) HBCs are not precursors ofolfactory neurons; (ii) there is a lineage path from GBCs tomature neurons; and (iii) sustentacular cells arise from a separatelineage.     

Diverse post-translational modifications of the pannexin family of channel-forming proteins

The pannexin family of channel-forming proteins is composed of 3 distinct but related members called Panx1, Panx2, and Panx3. Pannexins have been implicated in many physiological processes as well as pathological conditions, primarily through their function as ATP release channels. However, it is currently unclear if all pannexins are subject to similar or different post-translational modifications as most studies have focused primarily on Panx1. Using in vitro biochemical assays performed on ectopically expressed pannexins in HEK-293T cells, we confirmed that all 3 pannexins are N-glycosylated to different degrees, but they are not modified by sialylation or O-linked glycosylation in a manner that changes their apparent molecular weight. Using cell-free caspase assays, we also discovered that similar to Panx1, the C-terminus of Panx2 is a substrate for caspase cleavage. Panx3, on the other hand, is not subject to caspase digestion but an in vitro biotin switch assay revealed that it was S-nitrosylated by nitric oxide donors. Taken together, our findings uncover novel and diverse pannexin post-translational modifications suggesting that they may be differentially regulated for distinct or overlapping cellular and physiological functions.     

Depolarized fluorescence photobleaching recovery

The effects of the fact that the laser sources typically used in fluorescence photobleaching recovery (FPR) experiments in the most commonly employed in-line microscope imaging geometries, are highly linearly polarized, are examined in some detail. The implications of the results, in particular for the interpretation of FPR data in complex cell membrane systems in terms of laterally mobile and immobile sub-populations of the labelled molecular species of concern, are discussed. Methods of experimentally eliminating the potentially major rotational diffusion-based artifacts, different from those appropriate to three-dimensional (solution or suspension) systems which require other than in-line geometries, are delineated.Abbreviations FPR fluorescence photobleaching recovery - FRAP fluorescence recovery after photobleaching - 2- and 3-D two- and three-dimensional     

Sequence and type-specific immunogenicity of the amino-terminal region of type 1 streptococcal M protein

The NH2-terminal sequence of type 1 M protein was determined by automated Edman degradation of purified polypeptide fragments extracted from whole streptococci by limited digestion with pepsin. Three polypeptide fragments were purified by slab gel electrophoresis on sodium dodecyl sulfate (SDS) polyacrylamide followed by electroelution. The purified fragments migrated as 28-, 25-, and 23.5-kDa fragments, respectively. Each of the fragments inhibited opsonization of a diluted antiserum prepared in rabbits by immunization with whole type 1 streptococci. The amino-terminal sequences of the peptide fragments were confirmed by comparison with the primary structure predicted from the nucleotide sequence of the type 1 M protein structural gene. The 28-kDa fragment contained the NH2-terminal asparagine residue of the processed type 1 M protein, whereas the NH2-terminal sequences of the 25- and 23.5-kDa peptides began at residues 27 and 36, respectively. A seven-residue periodicity with respect to polar and nonpolar residues was observed beginning at residue 22 and, therefore, the secondary structural potential of type 1 M protein is similar to that reported for other M proteins. In contrast to the other M proteins, however, identical repeats were rare, the longest sequence identity consisting of a three-amino acid acid sequence Lys-Asp-Leu at positions 30-32 repeated once at positions 65-67. A 23-residue synthetic peptide of the amino-terminus of the type 1 M protein evoked opsonic antibodies against type 1 streptococci. These results indicate that the NH2-terminal region of type 1 M protein retains the secondary structural characteristics of other M serotypes. Moreover, it contains epitopes that evoke protective immune responses. Our studies may have bearing in the development of safe and effective vaccines against group A streptococcal infections.     

In situ detection of early replication phases of a gemini virus in legume protoplasts

Protoplasts of Phaseolus vulgaris L. (Top Crop), infected with bean golden mosaic virus, were isolated and fixed by various methods for in situ hybridization. An iodine-125 labeled probe was made from the replicative form of the virus. The localization and quantitation was done by autoradiography. Cell wall removal lowered the background and allowed a more accurate analysis. RNase was used to eliminate the possibility of hybrids to RNA. The evidence suggests a sequence of virus movements starting from rough endoplasm reticulum, moving to the nuclear membrane, and finally with the highest concentration inside the nucleus.Abbreviations BGMV bean golden mosaic virus - rfBGMV or rfDNA replicative double-stranded DNA virus - ssDNA single-stranded virus