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An Arabidopsis syntaxin homologue isolated by functional complementation of a yeast pep12 mutant.

ABSTRACT: The syntaxin family of integral membrane proteins are thought to function as receptors for transport vesicles, with different isoforms of this family localized to various membranes throughout the cell. The yeast Pep12 protein is a syntaxin homologue which may function in the trafficking of vesicles from the trans-Golgi network to the vacuole. We have isolated an Arabidopsis thaliana cDNA by functional complementation of a yeast pep12 mutant. The Arabidopsis cDNA (aPEP12) potentially encodes a 31-kDa protein which is homologous to yeast Pep12 and to other members of the syntaxin family, indicating that this protein may function in the docking or fusion of transport vesicles with the vacuolar membrane in plant cells. Northern blot analysis indicates that the mRNA is expressed in all tissues examined, although at a very low level in leaves. The mRNA is found in all cell types in roots and leaves, as shown by in situ hybridization experiments. The existence of plant homologues of proteins of the syntaxin family indicates that the basic vesicle docking and fusion machinery may be conserved in plants as it is in yeast and mammals.

SUBMITTER: Bassham DC

PROVIDER: S-EPMC41319 | biostudies-other | 1995 Aug

REPOSITORIES: biostudies-other

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An Arabidopsis syntaxin homologue isolated by functional complementation of a yeast pep12 mutant.

Bassham D C DC Gal S S da Silva Conceição A A Raikhel N V NV

Proceedings of the National Academy of Sciences of the United States of America 19950801 16

The syntaxin family of integral membrane proteins are thought to function as receptors for transport vesicles, with different isoforms of this family localized to various membranes throughout the cell. The yeast Pep12 protein is a syntaxin homologue which may function in the trafficking of vesicles from the trans-Golgi network to the vacuole. We have isolated an Arabidopsis thaliana cDNA by functional complementation of a yeast pep12 mutant. The Arabidopsis cDNA (aPEP12) potentially encodes a 31 ...[more]

PMID: 7638178

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Project description:BackgroundMultiprotein-bridging factor 1 (MBF1) is a transcriptional co-activator that bridges a sequence-specific activator (basic-leucine zipper (bZIP) like proteins (e.g. Gcn4 in yeast) or steroid/nuclear-hormone receptor family (e.g. FTZ-F1 in insect)) and the TATA-box binding protein (TBP) in Eukaryotes. MBF1 is absent in Bacteria, but is well- conserved in Eukaryotes and Archaea and harbors a C-terminal Cro-like Helix Turn Helix (HTH) domain, which is the only highly conserved, classical HTH domain that is vertically inherited in all Eukaryotes and Archaea. The main structural difference between archaeal MBF1 (aMBF1) and eukaryotic MBF1 is the presence of a Zn ribbon motif in aMBF1. In addition MBF1 interacting activators are absent in the archaeal domain. To study the function and therefore the evolutionary conservation of MBF1 and its single domains complementation studies in yeast (mbf1Δ) as well as domain swap experiments between aMBF1 and yMbf1 were performed.ResultsIn contrast to previous reports for eukaryotic MBF1 (i.e. Arabidopsis thaliana, insect and human) the two archaeal MBF1 orthologs, TMBF1 from the hyperthermophile Thermoproteus tenax and MMBF1 from the mesophile Methanosarcina mazei were not functional for complementation of an Saccharomyces cerevisiae mutant lacking Mbf1 (mbf1Δ). Of twelve chimeric proteins representing different combinations of the N-terminal, core domain, and the C-terminal extension from yeast and aMBF1, only the chimeric MBF1 comprising the yeast N-terminal and core domain fused to the archaeal C-terminal part was able to restore full wild-type activity of MBF1.However, as reported previously for Bombyx mori, the C-terminal part of yeast Mbf1 was shown to be not essential for function. In addition phylogenetic analyses revealed a common distribution of MBF1 in all Archaea with available genome sequence, except of two of the three Thaumarchaeota; Cenarchaeum symbiosum A and Nitrosopumilus maritimus SCM1.ConclusionsThe absence of MBF1-interacting activators in the archaeal domain, the presence of a Zn ribbon motif in the divergent N-terminal domain of aMBF1 and the complementation experiments using archaeal- yeast chimeric proteins presented here suggests that archaeal MBF1 is not able to functionally interact with the transcription machinery and/or Gcn4 of S. cerevisiae. Based on modeling and structural prediction it is tempting to speculate that aMBF1 might act as a single regulator or non-essential transcription factor, which directly interacts with DNA via the positive charged linker or the basal transcription machinery via its Zn ribbon motif and the HTH domain. However, also alternative functions in ribosome biosynthesis and/or functionality have been discussed and therefore further experiments are required to unravel the function of MBF1 in Archaea.

Dataset Information

An Arabidopsis syntaxin homologue isolated by functional complementation of a yeast pep12 mutant.

Publications

An Arabidopsis syntaxin homologue isolated by functional complementation of a yeast pep12 mutant.

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