Identification of a new gene in an operon for cellulose biosynthesis in Acetobacter xylinum

DNA sequencing of the region downstream of the cellulose synthase catalytic subunit gene of Acetobacter xylinum led to the identification of an open reading frame coding for a polypeptide of 86 kDa. The deduced amino acid sequence of this polypeptide matches from position 27 to 40 with the N-terminal amino acid sequence determined for a 93 kDa polypeptide that copurifies with the cellulose synthase catalytic subunit during purification of cellulose synthase. The cellulose synthase catalytic subunit gene and the gene encoding the 93 kDa polypeptide, along with other genes probably, are organized as an operon for cellulose biosynthesis in which the first gene is the catalytic subunit gene and the second gene codes for the 93 kDa polypeptide. The function of the 93 kDa polypeptide is not clear at present, however it appears to be tightly associated with the cellulose synthase catalytic subunit. Sequence analysis of the polypeptide shows that it is a membrane protein with a signal sequence at the N-terminal end and a transmembrane helix in the C-terminal region for anchoring it into the membrane.     

Sequence analysis of two exons from the murine dystrophin locus

We have isolated two genomic clones from the murine dystrophin locus, containing single exons encoding protein sequence from the putative actin-binding domain of the amino-terminus and the terminal portion of the triple helical domain. Using interspecific backcross progeny mice, both clones were shown to be X-linked. Sequence analysis indicated that the amino-terminal clone contains a 173 bp exon exhibiting 90% nucleotide sequence identity to human dystrophin exon 6, whilst the C-terminal clone contains a 61 bp exon with 93% nucleotide sequence identity to the human cDNA sequence.

     

Mouse Chromosome 7

Chair of Committee for Mouse Chromosome 7     

Development of left/right handedness in the chick heart.

The chick heart tube develops from the fusion of the right and left areas of precardiac mesoderm and in almost all cases loops to the embryo's right-hand side. We have investigated whether any intrinsic difference exists in the right and left areas of precardiac mesoderm, that influences the direction of looping of the heart tube. Chick embryos incubated to stages 4,5 and 6 were cultured by the New method. Areas of precardiac mesoderm were exchanged between donor and host embryos of the same stage and different stages to form control, double-right and double-left sided embryos. Overall, double-right sided embryos formed many more left-hand loops than double-left sided embryos. At stages 4 and 5 a small percentage of double-right embryos formed left-hand loops (13%) whereas at stage 6 almost 50% of hearts had left-hand loops. Control embryos formed right-hand loops in 97% of cases. The stability of right-hand heart looping by double-left sided embryos, may be related to the process of 'conversion', whereas the direction of looping by double-right sided embryos has become randomised. There is some indication that an intrinsic change occurred in the precardiac mesoderm between stages 5 and 6 that later influenced the direction of looping of the heart tube. The direction of body turning is suggested to be linked to the direction of heart looping.     

Closure of potassium M-channels by muscarinic acetylcholine-receptor stimulants requires a diffusible messenger.

The M-current (IK(M)) is a slow voltage-gated K+ current which can be inhibited by muscarinic acetylcholine-receptor (mAChR) agonists. In the present experiments we have tested whether this inhibition results from a local (membrane-delimited) interaction between the receptor and adjacent channels, or whether channel closure is mediated by a diffusible messenger. To do this, single KM(+)-channel currents were recorded from membrane patches in dissociated rat superior cervical sympathetic neurons by using cell-attached patch electrodes. Channel activity was inhibited when muscarine was applied to the cell membrane outside the patch but persisted when channels were exposed to muscarine added to the pipette solution. We conclude that a diffusible molecule (or molecules) is (are) required to induce intrapatch channel closure following activation of extra-patch receptors.     

Introduction of exogenous DNA into Chlamydomonas reinhardtii by electroporation.

The fate of exogenous DNA introduced into Chlamydomonas reinhardtii by electroporation was analyzed. With single and double electrical pulses, plasmids as large as 14 kb were introduced into cells with and without intact cell walls. Within hours after introduction, exogenous plasmid DNA was associated with nuclei isolated from cells; several weeks after introduction, exogenous DNA was stably integrated into the Chlamydomonas genome. These studies establish electroporation as a method for introducing DNA, and potentially other molecules, into C. reinhardtii.     

Evolutionary conservation of the spliceosomal protein, U2B''''.

U1 and U2snRNPs play key roles in pre-mRNA splicing. The interactions between the U1 and U2snRNP-specific proteins, U1A, U2A' and U2B' and their respective UsnRNAs are of interest both to elucidate their roles in splicing, and as models to study RNA-protein interactions. We have cloned a full-length cDNA, encoding U2B', from potato. This is the first report of a sequence for a plant UsnRNP protein. The plant U2B' sequence exhibits extensive similarity with the human U2B' protein at both the DNA and amino acid levels. The evolutionary conservation at the protein level, particularly in sequences implicated in determining specific binding to U2snRNA, suggests conservation of U2B' function from plants to man. The significance of amino acid substitutions in the RNP-80 motif with respect to U2snRNA binding in plants is discussed.     

The molecular mechanism of inhibition of alpha-type DNA polymerases by N2-(butylphenyl)dGTP and 2-(butylanilino)dATP: variation in susceptibility to polymerization.

Calf thymus DNA polymerase alpha (pol alpha) and bacteriophage T4 DNA polymerase (pol T4) were exploited as model enzymes to investigate the molecular mechanism of inhibitory action of N2-(p-n-butylphenyl)dGTP (BuPdGTP) and 2-(p-n-butyl-anilino)dATP (BuAdATP) on the BuPdNTP-susceptible alpha polymerase family. Kinetic analysis of inhibition of pol alpha with mixtures of complementary and noncomplementary template:primers indicated that both nucleotides induced the formation of a polymerase: inhibitor:primer-template complex. Primer extension experiments using the guanine form as the model analog indicated that pol alpha cannot utilize these nucleotides to extend primer termini. In contrast, pol T4 polymerized BuPdGTP, indicating that resistance to polymerization is not a common feature of the inhibitor mechanism among the broad membership of the alpha polymerase family.