Biology subjects

Neiman, A. M.

Publications and source records attributed to Neiman, A. M..

3 recordsLinked to original sources

bioRxiv2024

An acidic loop in the FHA domain of the yeast meiosis-specific kinase Mek1 interacts with a specific motif in a subset of Mek1 substrates

The meiosis-specific kinase Mek1 regulates key steps in meiotic recombination in the budding yeast, Saccharomyces cerevisiae. MEK1 limits resection at the double strand break (DSB) ends and is required for preferential strand invasion into homologs, a process known as interhomolog bias. After strand invasion, MEK1 promotes phosphorylation of the synaptonemal complex protein Zip1 that is necessary for DSB repair mediated by a crossover specific pathway that enables chromosome synapsis. In addition, Mek1 phosphorylation of the meiosis-specific transcription factor, Ndt80, regulates the meiotic recombination checkpoint that prevents exit from pachytene when DSBs are present. Mek1 interacts with Ndt80 through a five amino acid sequence, RPSKR, located between the DNA binding and activation domains of Ndt80. AlphaFold Multimer modeling of a fragment of Ndt80 containing the RPSKR motif and full length Mek1 indicated that RPSKR binds to an acidic loop located in the Mek1 FHA domain, a non-canonical interaction with this motif. A second protein, the 5-3 helicase Rrm3, similarly interacts with Mek1 through an RPAKR motif and is an in vitro substrate of Mek1. Genetic analysis using various mutants in the MEK1 acidic loop validated the AlphaFold model, in that they specifically disrupt two-hybrid interactions with Ndt80 and Rrm3. Phenotypic analyses further showed that the acidic loop mutants are defective in the meiotic recombination checkpoint, and in certain circumstances exhibit more severe phenotypes compared to the NDT80 mutant with the RPSKR sequence deleted, suggesting that additional, as yet unknown, substrates of Mek1 also bind to Mek1 using an RPXKR motif. ARTICLE SUMMARYThe FHA domain is conserved module best known for creating protein complexes by binding to phosphorylated threonines on target proteins. This work identified a non-canonical mechanism by which the FHA domain of the yeast meiosis-specific kinase Mek1 interacts with two of its substrates, Ndt80 and Rrm3. An acidic loop within the FHA domain binds to RPXKR motifs in Ndt80 and Rrm3. Genetic evidence suggests that this FHA domain acidic loop is required binding to additional Mek1 substrates.

genetics↗

bioRxiv2021

A conserved machinery underlies the synthesis of a chitosan layer in the Candida chlamydospore cell wall

The polysaccharide chitosan is found in the cell wall of specific cell types in a variety of fungal species where it contributes to stress resistance, or in pathogenic fungi, virulence. Under certain growth conditions, the pathogenic yeast Candida dubliniensis forms a cell type termed a chlamydosospore, which has an additional internal layer in its cell wall as compared to hyphal or yeast cell types. We report that this internal layer of the chlamydospore wall is rich in chitosan. The ascospore wall of Saccharomyces cerevisiae also has a distinct chitosan layer. As in S. cerevisiae, formation of the chitosan layer in the C. dubliniensis wall requires the chitin synthase CHS3 and the chitin deacetylase CDA2. In addition, three lipid droplet-localized proteins Rrt8, Srt1, and Mum3, identified in S. cerevisiae as important for chitosan layer assembly in the ascospore wall, are required for the formation of the chitosan layer of the chlamydospore wall in C. dubliniensis. These results reveal that a conserved machinery is required for the synthesis of a distinct chitosan layer in the walls of these two yeasts and may be generally important for incorporation of chitosan into fungal walls. ImportanceThe cell wall is the interface between the fungal cell and its environment and disruption of cell wall assembly is an effective strategy for antifungal therapies. Therefore, a detailed understanding of how cell walls form is critical to identify potential drug targets and develop therapeutic strategies. This work shows that a set of genes required for assembly of a chitosan layer in the cell wall of S. cerevisiae is also necessary for chitosan formation in a different cell type in a different yeast, C. dubliniensis. Because chitosan incorporation into the cell wall can be important for virulence, the conservation of this pathway suggests possible new targets for antifungals aimed at disrupting cell wall function.

cell biology↗

bioRxiv2020

A non-canonical Hippo pathway regulates spindle disassembly and cytokinesis during meiosis in Saccharomyces cerevisiae

Meiosis in the budding yeast Saccharomyces cerevisiae is used to create haploid yeast spores from a diploid mother cell. During meiosis II, cytokinesis occurs by closure of the prospore membrane, a membrane that initiates at the spindle pole body and grows to surround each of the haploid meiotic products. Timely prospore membrane closure requires SPS1, which encodes a STE20-family GCKIII kinase. To identify genes that may activate SPS1, we utilized a histone phosphorylation defect of sps1 mutants to screen for genes with a similar phenotype and found that cdc15 shared this phenotype. CDC15 encodes a Hippo-like kinase that is part of the mitotic exit network. We find that Sps1 complexes with Cdc15, that Sps1 phosphorylation requires Cdc15, and that CDC15 is also required for timely prospore membrane closure. We also find that SPS1, like CDC15, is required for meiosis II spindle disassembly and sustained anaphase II release of Cdc14 in meiosis. However, the NDR-kinase complex encoded by DBF2/DBF20 MOB1 which functions downstream of CDC15 in mitotic cells, does not appear to play a role in spindle disassembly, timely prospore membrane closure, or sustained anaphase II Cdc14 release. Taken together, our results suggest that the mitotic exit network is rewired for exit from meiosis II, such that SPS1 replaces the NDR-kinase complex downstream of CDC15.

cell biology↗