Biology subjects

Holetz, F. B.

Publications and source records attributed to Holetz, F. B..

3 recordsLinked to original sources

bioRxiv2026

The trypanosome mRNA decapping enzyme ALPH1 prefers caps without m7G methylation and produces diphosphate-RNA

5'ends of eukaryotic mRNAs are protected by the m7G cap, connected to the mRNA via a three-phosphate-bridge. In mRNA decay, the pyrophosphate bond between the and {beta} phosphate is cleaved by the nudix hydrolase DCP2. Uniquely among eukaryotes, Kinetoplastida lack DCP2 and instead employ the ApaH-like phosphatase ALPH1 for mRNA decapping. ALPH1 consists of an unstructured N-terminus, a catalytic domain and a structured C-terminus that mediates ALPH1 dimerisation. Here, we have analysed Trypanosoma brucei ALPH1 in greater detail. We find that the enzyme has broad substrate specificity and accepts different cap types and even cap analogues. Strikingly, cap-analogues and RNAs without the m7G-methyl group are turned over significantly faster than m7G methylated substrates. Moreover, all methylated and non-methylated cap analogues tested, with at least one additional nucleotide 3' to the NpppN moiety are cleaved at the {beta}-{gamma} pyrophosphate bond, producing the equivalent to a 5 diphosphate-RNA. While the presence of the ALPH1 C-terminal domain is essential for cell viability and increases enzyme activity in vitro, substrate preferences are determined solely by the catalytic domain. Altogether, these ALPH1 enzymatic properties exhibit intriguing differences to the canonical eukaryotic decapping enzyme DCP2, which we critically discuss and which potentially have biotechnological applications.

molecular biology↗

bioRxiv2024

Two distinct Trypanosoma eIF4F complexes co-exist, bind different mRNAs and are regulated during nutritional stress

Many eIF4F subunits and PABP paralogues are found in trypanosomes: six eIF4E, five eIF4G, one eIF4A and two PABPs. They are expressed simultaneously and assemble into different complexes, contrasting the situation in metazoans that use distinct complexes in different cell types or developmental stages. Each eIF4F complex has its own proteins, mRNAs and, consequently, a distinct function. We set out to study the function and regulation of the two major eIF4F complexes of Trypanosoma cruzi and identified the associated proteins and mRNAs of eIF4E3 and eIF4E4 in cells in exponential growth and in nutritional stress. Upon stress, eIF4G/eIF4A and PABP remain associated to the eIF4E, but the associations with other 43S pre-initiation factors decrease, indicating that ribosome attachment is impaired. Most eIF4E3-associated mRNAs encode for metabolic proteins, while eIF4E4 associate to mRNAs encoding ribosomal proteins. Interestingly, for both eIF4E3/4, more mRNAs were associated in stressed cells than in non-stressed cells, even though these mRNAs have lower translational efficiencies in stress. In summary, trypanosomes have two co-existing eIF4F complexes involved in translation of distinct mRNA cohorts important for growth. Under stress conditions, both complexes exit translation but remain bound to their mRNA targets.

molecular biology↗

bioRxiv2023

Leishmania Ribosomal Protein (RP) paralogous genes compensate each others expression maintaining protein native levels

In the protozoan parasite Leishmania, most of the genes encoding for ribosomal proteins (RPs) are present as two or more copies in the genome, their untranslated regions (UTRs) are predominantly divergent, and might be associated with a distinct regulation of the paralogous genes expression. Here, we investigated the expression profiles of two RPs (S16 and L13a) encoded by duplicated genes in Leishmania major. The genes encoding for S16 protein have identical CDSs and divergent UTRs while the L13a CDSs diverge in two amino acids with divergent UTRs. Using CRISPR/Cas9 genomic editing system, we generated knockout ({Delta}) and tagged transfectants for each paralog of L13a and S16. Combining tagged and {Delta} cell lines we show that the expression of both RPS16 and RPL13a isoforms differ throughout the parasite development with one of the isoforms being always more abundant than its respective copy. Additionally, compensatory expression was observed for each paralog when one of the isoforms was deleted, evidencing functional conservation of these proteins. Such phenomenon is related to post-translational processes, since the compensation happened at the protein levels, with no alterations observed at the transcript levels. Ribosomal profiles for RPL13a point out a standard behavior for these paralogues as already reported for other RPs in trypanosomatids, showing its interaction with heavy RNA-protein complexes. The identification of sets of proteins binding specifically to the 3UTRs of either the high or less abundant transcripts suggests a possible role of these proteins to differently control the levels of expression of these RP genes. In addition, conserved cis-elements were identified in the 3UTRs of RPS16 or RPL13a; among these, exclusive cis-elements for the more or for the less expressed transcripts were identified.

molecular biology↗