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Molecular and Cellular Biology, August 2007, p. 5456-5467, Vol. 27, No. 15
0270-7306/07/$08.00+0     doi:10.1128/MCB.00416-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Mek1 Kinase Is Regulated To Suppress Double-Strand Break Repair between Sister Chromatids during Budding Yeast Meiosis

Hengyao Niu,¹ Xue Li,^2, Emily Job,¹ Caroline Park,¹ Danesh Moazed,² Steven P. Gygi,² and Nancy M. Hollingsworth^1*

Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York 11794-5215,¹ Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115²

Received 9 March 2007/ Returned for modification 2 April 2007/ Accepted 8 May 2007

Mek1 is a meiosis-specific kinase in budding yeast which promotes recombination between homologous chromosomes by suppressing double-strand break (DSB) repair between sister chromatids. Previous work has shown that in the absence of the meiosis-specific recombinase gene, DMC1, cells arrest in prophase due to unrepaired DSBs and that Mek1 kinase activity is required in this situation to prevent repair of the breaks using sister chromatids. This work demonstrates that Mek1 is activated in response to DSBs by autophosphorylation of two conserved threonines, T327 and T331, in the Mek1 activation loop. Using a version of Mek1 that can be conditionally dimerized during meiosis, Mek1 function was shown to be promoted by dimerization, perhaps as a way of enabling autophosphorylation of the activation loop in trans. A putative HOP1-dependent dimerization domain within the C terminus of Mek1 has been identified. Dimerization alone, however, is insufficient for activation, as DSBs and Mek1 recruitment to the meiosis-specific chromosomal core protein Red1 are also necessary. Phosphorylation of S320 in the activation loop inhibits sister chromatid repair specifically in dmc1-arrested cells. Ectopic dimerization of Mek1 bypasses the requirement for S320 phosphorylation, suggesting this phosphorylation is necessary for maintenance of Mek1 dimers during checkpoint-induced arrest.

Published ahead of print on 25 May 2007.

Present address: Amgen Inc., 4000 Nelson Road, Longmont, CO 80503.

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