Cherryl Hunt

The nature of the clear zone around microtubules

SummaryThe clear zones seen around microtubules in transverse sections of nutritive tubes vary in size depending on whether a microtubule is bordered by ribosomes or by another microtubule. We consider that such a finding is not consistent with the current view, that the clear zone is maintained by microtubule-associated material. It can, however, be accounted for by an electrostatic repulsion between the surfaces of negatively charged microtubules and between microtubules and ribosomes which are also negatively charged. The experiments presented here, involving on the one hand the addition of cationic substances to microtubules and on the other the alteration in charge of the microtubules, support this hypothesis.

Microtubule polarity in the nutritive tubes of insect ovarioles.

SummaryThe enormous numbers of microtubules within the nutritive tubes of hemipteran ovarioles are amenable to the hook-decoration technique for determining microtubule structural polarity, as they can be microdissected from ovarioles intact. This has allowed the correlation between the polarity of this continuously elongating complex of microtubules within a nutritive tube and the direction of transport along its length; and has shown that the plus or fast growing ends of the microtubules are all situated at the anterior end of a nutritive tube proximal to the trophic region from which synthesised materials are passed back towards the developing oocytes.

Subtelomeric sequence from the right arm of Schizosaccharomyces pombe chromosome I contains seven permease genes

The sequence has been determined of 80 888 bp of contiguous subtelomeric DNA, including the isp5 gene, from the right arm of chromosome I of Schizosaccharomyces pombe; 27 open reading frames (ORFs) longer than 100 codons are present, giving a density of one gene per 3.0 kb. Seven of the predicted proteins are members of the major facilitator superfamily (MFS) of transport proteins, including four amino acid permease homologues, bringing this family of amino acid permease sequences to 17 in Sz. pombe, and a phylogenetic analysis is presented. Also encoded is an allantoate permease homologue, a sulphate permease homologue and a probable urea active transporter. Predicted non‐membrane proteins include a 1‐aminocyclopropane‐1‐carboxylate deaminase (ACC deaminase), a class III aminotransferase, serine acetyltransferase, protein‐L‐isoaspartate O‐methyltransferase, α‐glucosidase, α‐galactosidase, esterase/lipase, oxidoreductase of the short‐chain dehydrogenase/reductase (SDR) family, aldehyde dehydrogenase, formamidase, amidase, flavohaemoprotein, a putative translation initiation inhibitor and a protein with similarity to a filamentous fungal conidiation‐specific protein. The remaining six ORFs are likely to encode proteins, either because they have sequence similarity with hypothetical proteins or because they are known to be transcribed. Introns are scarce in the sequenced region: only three ORFs contain introns, with only one having multiple introns. The sequenced region also contains a single Tf1 transposon long terminal repeat (LTR). The sequence is derived from cosmid clones c869, c922 and c1039 and has been submitted to the EMBL database under entries SPAC869 (Accession No. AL132779), SPAC922 (AL133522) and SPAC1039 (AL133521). Copyright

Protein turnover in the cytoplasmic transport system within an insect ovary - a clue to the mechanism of microtubule-associated transport

The movement of radioactively labelled polypeptides into the microtubule‐associated transport channels in the ovaries of a hemipteran insect has been analysed using SDS‐polyacrylamide slab gel electrophoresis and fluorography. The patterns of label suggest that the microtubules which pack the transport channels form a relatively static cytoskeleton while other components move independently from them along the channels. As well as illustrating the functional organisation of microtubule‐associated transport in this system our studies of labelled proteins have also provided clues as to the mechanism of transport itself.

Binding of axonemal dynein to microtubules comprising the cytoplasmic transport system in insect ovarioles

Dynein isolated from ciliary axonemes of Tetrahymena is shown to bind in a characteristic fashion as arms to microtubules dissected from the nutritive tubes of insect ovarioles. The microtubules in nutritive tubes are associated with the transport of cytoplasmic components along their length, and the significance of their ability to bind axonemal dynein, to the possibility that microtubule/dynein interactions are involved in microtubule-associated movements, generally, is discussed.

MAPs and motors in insect ovaries

Summary MAPs and microtubule motor proteins from the massive microtubule translocation complexes within the ovaries of hemipteran insects have been identified and characterized. Both classes of proteins have been compared with those of other systems, and the function of both in the insect ovaries is speculated upon.

High molecular weight microtubule-associated proteins within testes of hemipteran insects

Results presented here indicate that the high molecular weight microtubule-associated proteins isolated from the ovaries of the hemipterans, Oncopeltus fasciatus and Notonecta glauca, while absent from nervous tissue, are present in the testes of the respective species. Here they are seen to be located to extensive microtubule aggregates within the cells surrounding the sperm, but not obviously to the sperm themselves.

The mei3 region of the Schizosaccharomyces pombe genome.

Expression of the mei3 gene is sufficient to induce meiosis in the fission yeast Schizosaccharomyces pombe. The mei3 gene is located 0.64 Mb from the telomere of the left arm of Sz. pombe chromosome II. We have sequenced and analysed 107 kb of DNA from the mei3 genomic region. The sequence includes 14 known genes (bag1‐B, csh3, dps1, gpt1, mei3, mfm3, pac1, prp31, rpl38‐1, rpn3, rti1, spa1, spm1 and ubc4) and 26 other open reading frames (ORFs) longer than 100 codons: a density of one protein‐coding gene per 2.7 kb. Twenty‐one of the 40 ORFs (53%) have introns. In addition there is one lone Tf1 transposon long terminal repeat (LTR), tRNATrp and tRNASer genes and a 5S rRNA gene. 14 of the novel ORFs show sequence similarities which suggest functions of their products, including a coatomer α‐subunit, a catechol O‐methyltransferase, protein kinase, asparagine synthetase, zinc metalloprotease, acetyltransferase, phosphatidylinositol 4‐kinase, inositol polyphosphate phosphatase, GTPase‐activating protein, permease, pre‐mRNA splicing factor, 20S proteasome component and a thioredoxin‐like protein. One predicted protein has similarity to the human Cockayne syndrome protein CSA and one with human GTPase XPA binding protein XAB1. Three ORFs are likely to code for proteins because they have sequence similarity with hypothetical proteins, three encode predicted coiled‐coil proteins and four are sequence orphans. The sequence is derived from cosmid clones c4664, c119 and c557 and has been submitted to the EMBL database under Accession Nos AL591302, AL022117, AL110506 and AL023634 (part). Copyright

The mating-type region of Schizosaccharomyces pombe h(-S) 972: sequencing and analysis of 69 kb including the expressed mat1 locus.

The sequence has been determined of 68 897 bp of genomic DNA including the expressed mat1 mating‐type locus from Schizosaccharomyces pombe h−S strain 972. The DNA sequence, located on the long arm of fission yeast chromosome II and contained in two cosmid clones, was analysed to reveal one autonomously replicating sequence, two retrotransposon long terminal repeats (LTRs), one tRNAGly gene and 33 open reading frames (ORFs), of which 15 contain introns. Nine of these ORFs code for previously described genes (trt1, rpl10, rps21, nif1, sui1 (psu1), matMi, matMc, let1 and rpa4), one of which (trt1) contains 15 introns, the highest number yet recorded in a gene of S. pombe. Of the remaining 24 ORFs, sequence similarity suggests that the function of 13 of the encoded proteins may be predicted and these include four mitochondrial proteins, two transport proteins, two signalling molecules, a component of serine palmitolytransferase, a homologue of 3‐methyladenine DNA glycosylase, a multifunctional alcohol dehydrogenase, a killer toxin sensitivity factor and an acetyl transferase. Six deduced sequences appear to be related to proteins of unknown function in Saccharomyces cerevisiae or S. pombe and the remaining five are hypothetical proteins. This sequence has been submitted to the EMBL database under the following entries: SPBC23G7 (Accession No. AL035065), SPBC18E5 (AL035077) and SPBC29A3 (part) (AL022299). Copyright