B79
Evidence that histone H2A phosphorylation and histone H3 methylation help recruit Rad9 to uncapped Saccharomyces cerevisiae telomeres
Peter Banks, David Lydall
Newcastle University, Newcastle upon Tyne, UK
The telomere is a specialised DNA protein complex comprised of several proteins that regulate elongation and protection of DNA at the end of linear chromosomes. Proteins such as Cdc13 bind to the end of chromosomes forming a cap. When capping mechanisms are defective the exposed DNA is treated in a manner analogous to the repair of double stranded DNA breaks resulting in resection of the DNA to produce single stranded DNA and homologous recombination. Such DNA repair mechanisms acting at telomeres can lead to chromosomal rearrangements and to cancer.
To study the response to telomere uncapping we utilise a temperature sensitive Saccharomyces cerevisiae strain containing the cdc13-1 point mutation within the CDC13 gene. At temperatures of 28°C and above S. cerevisiae containing this mutation arrest at the G2/M phase boundary. The growth of cdc13-1 mutants can be partially rescued by inactivating genes involved in creating single stranded DNA or signalling DNA damage such as EXO1 or RAD9 respectively. Transient phosphorylation of histone H2A at serine 129 is one of the earliest events occuring after DNA damage whilst methylation of histone H3 at lysine 79 by Dot1 is constitutive.
Our experiments show that mutation of serine 129 to a non-phosphorylatable alanine residue and inactivation of the histone methyltransferase DOT1 both partially rescue the temperature sensitivity of the cdc13-1 mutant by affecting the integrity of the G2/M phase checkpoint. We are testing the hypothesis that H2A S129 phosphorylation and Dot1 dependant histone methylation independently recruit the checkpoint protein Rad9 to uncapped telomeres.
