Biomedical subjects

Ann Sutton

Publications and source records attributed to Ann Sutton.

8 recordsLinked to original sources

PubMed2006

C2H2 zinc finger-SET histone methyltransferase is a plant-specific chromatin modifier.

Histone modification represents a universal mechanism for regulation of eukaryotic gene expression underlying diverse biological processes from neuronal gene expression in mammals to control of flowering in plants. In animal cells, these chromatin modifications are effected by well-defined multiprotein complexes containing specific histone-modifying activities. In plants, information about the composition of such co-repressor complexes is just beginning to emerge. Here, we report that two Arabidopsis thaliana factors, a SWIRM domain polyamine oxidase protein, AtSWP1, and a plant-specific C2H2 zinc finger-SET domain protein, AtCZS, interact with each other in plant cells and repress expression of a negative regulator of flowering, FLOWERING LOCUS C (FLC) via an autonomous, vernalization-independent pathway. Loss-of-function of either AtSWP1 or AtCZS results in reduced dimethylation of lysine 9 and lysine 27 of histone H3 and hyperacetylation of histone H4 within the FLC locus, in elevated FLC mRNA levels, and in moderately delayed flowering. Thus, AtSWP1 and AtCZS represent two main components of a co-repressor complex that fine tunes flowering and is unique to plants.

Amino Acid Sequence↗

PubMed2006

SirT2 is a histone deacetylase with preference for histone H4 Lys 16 during mitosis.

The mammalian cytoplasmic protein SirT2 is a member of the Sir2 family of NAD+-dependent protein deacetylases involved in caloric restriction-dependent life span extension. We found that SirT2 and its yeast counterpart Hst2 have a strong preference for histone H4K16Ac in their deacetylation activity in vitro and in vivo. We have pinpointed the decrease in global levels of H4K16Ac during the mammalian cell cycle to the G2/M transition that coincides with SirT2 localization on chromatin. Mouse embryonic fibroblasts (MEFs) deficient for SirT2 show higher levels of H4K16Ac in mitosis, in contrast to the normal levels exhibited by SirT1-deficient MEFs. The enzymatic conversion of H4K16Ac to its deacetylated form may be pivotal to the formation of condensed chromatin. Thus, SirT2 is a major contributor to this enzymatic conversion at the time in the cell's life cycle when condensed chromatin must be generated anew.

Animals↗

PubMed2006

The BUR1 cyclin-dependent protein kinase is required for the normal pattern of histone methylation by SET2.

BUR1 and BUR2 encode the catalytic and regulatory subunits of a cyclin-dependent protein kinase complex that is essential for normal growth and has a general role in transcription elongation. To gain insight into its specific role in vivo, we identified mutations that reverse the severe growth defect of bur1Delta cells. This selection identified mutations in SET2, which encodes a histone methylase that targets lysine 36 of histone H3 and, like BUR1, has a poorly characterized role during transcription elongation. This genetic relationship indicates that SET2 activity is required for the growth defect observed in bur1Delta strains. This SET2-dependent growth inhibition occurs via methylation of histone H3 on lysine 36, since a methylation-defective allele of SET2 or a histone H3 K36R mutation also suppressed bur1Delta. We have explored the relationship between BUR1 and SET2 at the biochemical level and find that histone H3 is monomethylated, dimethylated, and trimethylated on lysine 36 in wild-type cells, but trimethylation is significantly reduced in bur1 and bur2 mutant strains. A similar methylation pattern is observed in RNA polymerase II C-terminal domain truncation mutants and in an spt16 mutant strain. Chromatin immunoprecipitation assays reveal that the transcription-dependent increase in trimethylated K36 over open reading frames is significantly reduced in bur2Delta strains. These results establish links between a regulatory protein kinase and histone methylation and lead to a model in which the Bur1-Bur2 complex counteracts an inhibitory effect of Set2-dependent histone methylation.

Alleles↗

PubMed2005

A yeast polyamine acetyltransferase.

An uncharacterized yeast gene has been shown to encode a polyamine acetyltransferase and named PAA1. The recombinant Paa1 protein readily acetylates various polyamines such as putrescine, spermidine, and spermine. paa1 mutants are viable and grow normally under standard conditions. The mutants are sensitive to hydroxyurea, and they are synthetically temperature-sensitive with a rad53-21 mutation. The mutants also show genetic interactions with components of the transcriptional co-activator complex, SAGA, and partially suppress Spt- phenotypes of two spt mutants. These phenotypes suggest that acetylation of polyamines removes them from chromatin and makes the chromatin more accessible. It is known that spermine, but not acetyl spermine, is a precursor in the pathway for synthesis of coenzyme A in yeast. When Paa1 is overexpressed, leading to a lower level of spermine, cells show a growth dependence on either of two downstream compounds in the coenzyme A pathway, pantothenate or beta-alanine. This demonstrates that spermine and perhaps other polyamines are the in vivo targets of Paa1.

Acetyltransferases↗

PubMed2005

The language abilities of bilingual children with Down syndrome.

Children with Down syndrome (DS) have cognitive disabilities resulting from trisomy 21. Language-learning difficulties, especially expressive language problems, are an important component of the phenotype of this population. Many individuals with DS are born into bilingual environments. To date, however, there is almost no information available regarding the capacity of these individuals to acquire more than 1 language. The present study compared the language abilities of 8 children with DS being raised bilingually with those of 3 control groups matched on developmental level: monolingual children with DS (n = 14), monolingual typically developing (TD) children (n = 18), and bilingual TD children (n = 11). All children had at least 100 words in their productive vocabularies but a mean length of utterance of less than 3.5. The bilingual children spoke English and 1 other language and were either balanced bilinguals or English-dominant. English testing was completed for all children using the following: the Preschool Language Scale, Third Edition; language sampling; and the MacArthur Communicative Development Inventories (CDI). Bilingual children were also tested in the second language using a vocabulary comprehension test, the CDI, and language sampling. Results provided evidence of a similar profile of language abilities in bilingual children as has been documented for monolingual children with DS. There was no evidence of a detrimental effect of bilingualism. That is, the bilingual children with DS scored at least as well on all English tests as their monolingual DS counterparts. Nonetheless, there was considerable diversity in the second-language abilities demonstrated by these individuals with DS. Clinical implications are addressed.

Aptitude↗

PubMed2003

Sas4 and Sas5 are required for the histone acetyltransferase activity of Sas2 in the SAS complex.

The SAS2 gene is involved in transcriptional silencing in Saccharomyces cerevisiae. Based on its primary sequence, the Sas2 protein is predicted to be a member of the MYST family of histone acetyltransferases (HATs). Sas2 forms a complex with Sas4 and Sas5, which are required for its silencing function. Here we show that recombinant Sas2 has HAT activity that absolutely requires Sas4 and is stimulated by Sas5. The recombinant SAS complex acetylates H4 lysine 16 and H3 lysine 14. Furthermore, a purified SAS complex from yeast shows similar activity and specificity. In contrast to other MYST HATs, neither the recombinant nor the native SAS complex acetylated nucleosomal histones under conditions that were optimum for acetylating free histones. Finally, although the SAS subunits interact genetically and physically with Asf1, a histone deposition factor, association of H3 and H4 with Asf1 blocks their acetylation by the SAS complex, raising the possibility that the SAS HAT complex may acetylate free histones prior to their deposition onto DNA by Asf1 or CAF-I.

Acetylation↗

PubMed2003

Enp1, a yeast protein associated with U3 and U14 snoRNAs, is required for pre-rRNA processing and 40S subunit synthesis.

ENP1 is an essential Saccharomyces cerevisiae gene encoding a 483 amino acid polypeptide. Enp1 protein is localized in the nucleus and concentrated in the nucleolus. An enp1-1 temperature-sensitive mutant inhibited 35S pre-rRNA early processing at sites A(0), A(1) and A(2) as shown by northern analysis of steady state levels of rRNA precursors. Pulse-chase analysis further revealed that the enp1-1 strain was defective in the synthesis of 20S pre-rRNA and hence 18S rRNA, which led to reduced formation of 40S ribosomal subunits. Co-precipitation analysis revealed that Enp1 was associated with Nop1 protein, as well as with U3 and U14 RNAs, two snoRNAs implicated in early pre-rRNA processing steps. These results suggest a direct role for Enp1 in the early steps of rRNA processing.

Alleles↗

PubMed2003

Set2-catalyzed methylation of histone H3 represses basal expression of GAL4 in Saccharomyces cerevisiae.

Recent work has shown that histone methylation is an important regulator of transcription. While much is known about the roles of histone methyltransferases (HMTs) in the establishment of heterochromatin, little is known of their roles in the regulation of actively transcribed genes. We describe an in vivo role of the Saccharomyces cerevisiae HMT, Set2. We identified SET2 as a gene necessary for repression of GAL4 basal expression and show that the evolutionarily conserved SACI, SACII, and SET domains of Set2 are necessary for this repression. We confirm that Set2 catalyzes methylation of lysine 36 on the N-terminal tail of histone H3. Conversion of lysine 36 to an unmethylatable arginine causes a decrease in the repression of GAL4 transcription, as does a Delta set2 mutation. We further show that lysine 36 of histone H3 at GAL4 is methylated and that this methylation is dependent upon the presence of SET2.

Amino Acid Sequence↗