The EKC/KEOPS complex is universally conserved in Archaea and Eukarya and has been implicated in several cellular processes, including transcription, telomere homeostasis and genomic instability. ...However, the molecular function of the complex has remained elusive so far. We analyzed the transcriptome of EKC/KEOPS mutants and observed a specific profile that is highly enriched in targets of the Gcn4p transcriptional activator. GCN4 expression was found to be activated at the translational level in mutants via the defective recognition of the inhibitory upstream ORFs (uORFs) present in its leader. We show that EKC/KEOPS mutants are defective for the N6-threonylcarbamoyl adenosine modification at position 37 (t6A37) of tRNAs decoding ANN codons, which affects initiation at the inhibitory uORFs and provokes Gcn4 de-repression. Structural modeling reveals similarities between Kae1 and bacterial enzymes involved in carbamoylation reactions analogous to t6A37 formation, supporting a direct role for the EKC in tRNA modification. These findings are further supported by strong genetic interactions of EKC mutants with a translation initiation factor and with threonine biosynthesis genes. Overall, our data provide a novel twist to understanding the primary function of the EKC/KEOPS and its impact on several essential cellular functions like transcription and telomere homeostasis.
A survey of hydrophobic patches on the surface of 112 soluble, monomeric proteins is presented. The largest patch on each individual protein averages around 400 A2 but can range from 200 to 1,200 A2. ...These areas are not correlated to the sizes of the proteins and only weakly to their apolar surface fraction. Ala, Lys, and Pro have dominating contributions to the apolar surface for smaller patches, while those of the hydrophobic amino acids become more important as the patch size increases. The hydrophilic amino acids expose an approximately constant fraction of their apolar area independent of patch size; the hydrophobic residue types reach similar exposure only in the larger patches. Though the mobility of residues on the surface is generally higher, it decreases for hydrophilic residues with increasing patch size. Several characteristics of hydrophobic patches catalogued here should prove useful in the design and engineering of proteins.
The Saccharomyces cerevisiae Slx5/8 complex is the founding member of a recently defined class of SUMO-targeted ubiquitin ligases (STUbLs). Slx5/8 has been implicated in genome stability and ...transcription, but the precise contribution is unclear. To characterise Slx5/8 function, we determined genome-wide changes in gene expression upon loss of either subunit. The majority of mRNA changes are part of a general stress response, also exhibited by mutants of other genome integrity pathways and therefore indicative of an indirect effect on transcription. Genome-wide binding analysis reveals a uniquely centromeric location for Slx5. Detailed phenotype analyses of slx5 Delta and slx8 Delta mutants show severe mitotic defects that include aneuploidy, spindle mispositioning, fish hooks and aberrant spindle kinetics. This is associated with accumulation of the PP2A regulatory subunit Rts1 at centromeres prior to entry into anaphase. Knockdown of the human STUbL orthologue RNF4 also results in chromosome segregation errors due to chromosome bridges. The study shows that STUbLs have a conserved role in maintenance of chromosome stability and links SUMO-dependent ubiquitination to a centromere-specific function during mitosis.
Since July 1995, the European Bioinformatics Institute (EBI) has maintained RHdb (http://www.ebi.ac.uk/RHdb), a public database for radiation hybrid data. Radiation hybrid mapping is an important ...technique for determining high resolution maps. RHdb is also served by CORBA servers. The EBI is an Outstation of the European Molecular Biology Laboratory (EMBL).
Since July 1995, the European Bioinformatics Institute (EBI) has maintained RHdb (http://www.ebi.ac.uk/RHdb/RHdb.html), a public database for radiation hybrid data. Radiation hybrid mapping is an ...important technique for determining high resolution maps. Recently, CORBA access has been added to Rhdb. The EBI is an Outstation of the European Molecular Biology Laboratory (EMBL).
Since July 1995, the European Bioinformatics Institute (EBI) has maintained RHdb (http://www.ebi.ac.uk/RHdb ), a public database for radiation hybrid data. Radiation hybrid mapping is an important ...technique for determining high resolution maps. RHdb is also served by CORBA servers. The EBI is an Outstation of the European Molecular Biology Laboratory (EMBL).
Since July 1995, the European Bioinformatics Institute (EBI) has maintained the Radiation Hybrid database (RHdb; http://www.ebi.ac.uk/RHdb), a public database for radiation hybrid data. Radiation ...hybrid mapping is an important technique for determining high resolution maps. Recently, CORBA access has been added to RHdb. The EBI is an Outstation of the European Molecular Biology Laboratory (EMBL).
PDF
