The nuclear envelope and spindle pole body-associated Mps3 protein bind telomere regulators and function in telomere clustering

It has long been posited that the nuclear envelope is a key regulator of both the spatial organization of chromatin and gene transcription. Mps3p is an integral nuclear envelope membrane protein with a single trans-membrane domain that is essential for spindle pole body duplication. More recently, Mps3p was shown to associate with the cohesion establishment factor Ctf7p and found to be critical for cohesion establishment. Here, we provide new evidence that the nuclear envelope, via Mps3p, plays a pivotal role in telomere foci formation. Results from in vitro pull-downs and in vivo coprecipitations also show that Mps3p associates with the telomerase-assembly component Est1p. Moreover, pair-wise combinations of mps3, est1 or ctf7 alleles all produce conditional lethality. Findings that Mps3p and the nuclear envelope recruit/sequester soluble chromatin metabolism factors such as Ctf7p and Est1p describe, at the molecular level, a new mechanism of nuclear envelope-dependent chromatin regulation.