Biomedical subjects

A Hamal

Publications and source records attributed to A Hamal.

5 recordsLinked to original sources

PubMed1999

Plant MAP kinase kinase kinases structure, classification and evolution.

The increasing number of reports describing plant MAP kinase signalling components reflects the cardinal role that MAP kinase pathways are likely to play during plant growth and development. Relationship and structural analyses of plant MAP kinase kinase kinase related cDNAs and genes established, on one hand, the PMEKKs, which may be distinguished into the alpha, beta, gamma, and zeta groups, and, on the other hand, the PRAFs that consist of the delta, eta and theta groups. Plant MAP3Ks are characterized by different primary structures, but conserved within a single group. A relationship analysis, which included animal, fungal and plant MAP3Ks, revealed a high degree of diversity among this biochemically established set of proteins, thus suggesting a range of biological functions. Four major families emerged, namely the MEKK/STE11, including the PMEKKs, the RAF, including the PRAFs, as well as the MLK and CDC7 families. These four families showed phylum-dependent distributions. Signature sequences characterizing the RAF family and the RAF subfamilies have been evidenced. However, no equivalent sequence motifs were identified for the MEKK/STE11 family, which is highly heterogeneous.

Evolution, Molecular↗

PubMed1999

Characterisation of novel plant genes encoding MEKK/STE11 and RAF-related protein kinases.

Various elements of the MAP kinase module have been isolated in plants. We describe here the characterisation of 14 new plant cDNAs and genes encoding putative MAP kinase kinase kinases (MAP3Ks) related to the MEKK/STE11 and RAF protein kinases. Plant MAP3Ks are characterised by a variety of primary structures conserved within closely related proteins. Southern blot analysis suggests that plant MAP3Ks are heterogenous in their genomic structure, existing either as single copy genes or as small gene families. An RT-PCR analysis showed that in Arabidopsis thaliana, all organs studied contain detectable levels of transcripts of each of the MAP3K genes identified; however, signals obtained with mature pollen were weak or non-existent except for AtMAP3Kgamma. None of the reported genes share a cell-cycle or a cold stress regulated expression.

Amino Acid Sequence↗

PubMed1999

Molecular characterisation of plant cDNAs BnMAP4Kalpha1 and BnMAP4Kalpha2 belonging to the GCK/SPS1 subfamily of MAP kinase kinase kinase kinase.

Several yeast and mammal MAP kinase modules require, upstream of their MAP kinase kinase kinase (MAP3K), a MAP3K kinase (MAP4K). An Arabidopsis thaliana EST clone, sharing identity to MAP4Ks from yeast and mammals, has been used to isolate cDNA clones from a Brassica napus microspore-derived embryo cDNA library. The BnMAP4Kalpha1 and BnMAP4K-alpha2 clones encode putative proteins possessing the 12 subdomains of the serine/threonine protein kinase catalytic domain. A detailed analysis showed that they belong to the GCK/SPS1 subfamily of MAP4K proteins which possess an amino terminal catalytic domain and a long carboxy terminal tail. A Southern blot analysis suggested that the two proteins are encoded by a small multigene family. Expression studies revealed the presence of BnMAP4Kalpha1 and -alpha2 transcripts in all the tissues examined; however, they are most abundant in roots, siliques and flower buds. The expression of BnMAP4Kalpha1 and -alpha2 at the three main developmental stages of microspore-derived embryos (i.e., globular/heart, torpedo and cotyledonary) was confirmed by northern blot and RT-PCR analysis. An expression analysis of the above genes using synchronised Arabidopsis thaliana cell suspensions showed that the homologues genes are cell cycle regulated.

Amino Acid Sequence↗

PubMed1990

Purification and characterization of a DNA polymerase from the archaebacterium Thermoplasma acidophilum.

A thermophilic DNA polymerase has been purified to near homogeneity from the archaebacterium Thermoplasma acidophilum. Analysis of the purified enzyme by sodium dodecyl sulfate gel electrophoresis revealed a single polypeptide of 88 kDa which co-sediments with the DNA polymerase activity on sucrose gradients. Combination of sedimentation and gel filtration analyses indicates that this DNA polymerase is an 88-kDa monomeric enzyme in its native form. The DNA polymerase is resistant to aphidicolin, slightly sensitive to 2',3'-dideoxyribosylthymine triphosphate and inhibited by N-ethylmaleimide when preincubation with this reagent is performed at 65 degrees C. We find that a 3'----5' exonuclease activity is associated with the purified DNA polymerase; the two activities of the enzyme are optimal at 65 degrees C but the exonuclease activity is active in a broader range of lower temperatures and is more thermostable than the DNA polymerase activity.

Archaea↗

PubMed1989

Studies on DNA polymerases and topoisomerases in archaebacteria.

We have isolated DNA polymerases and topoisomerases from two thermoacidophilic archaebacteria: Sulfolobus acidocaldarius and Thermoplasma acidophilum. The DNA polymerases are composed of a single polypeptide with molecular masses of 100 and 85 kDa, respectively. Antibodies against Sulfolobus DNA polymerase did not cross react with Thermoplasma DNA polymerase. Whereas the major DNA topoisomerase activity in S. acidocaldarius is an ATP-dependent type I DNA topoisomerase with a reverse gyrase activity, the major DNA topoisomerase activity in T. acidophilum is a ATP-independent relaxing activity. Both enzymes resemble more the eubacterial than the eukaryotic type I DNA topoisomerase. We have found that small plasmids from halobacteria are negatively supercoiled and that DNA topoisomerase II inhibitors modify their topology. This suggests the existence of an archaebacterial type II DNA topoisomerase related to its eubacterial and eukaryotic counterparts. As in eubacteria, novobiocin induces positive supercoiling of halobacterial plasmids, indicating the absence of a eukaryotic-like type I DNA topoisomerase that relaxes positive superturns.

Archaea↗