1. Division of Biochemistry and Molecular Biology, Department of Molecular and Cell Biology, 401 Barker Hall, University of California, Berkeley, California 94720-3204, USA

Correspondence to: Kathleen Collins Correspondence and requests for materials should be addressed to J.R.M. (e-mail: Email: jmitch@uclink4.berkeley.edu) or K.C. (e-mail: Email: kcollins@socrates.berkeley.edu).

Abstract

The X-linked form of the human disease dyskeratosis congenita (DKC) is caused by mutations in the gene encoding dyskerin¹. Sufferers have defects in highly regenerative tissues such as skin and bone marrow, chromosome instability and a predisposition to develop certain types of malignancy. Dyskerin is a putative pseudouridine synthase, and it has been suggested that DKC may be caused by a defect in ribosomal RNA processing. Here we show that dyskerin is associated not only with H/ACA small nucleolar RNAs², but also with human telomerase RNA, which contains an H/ACA RNA motif³. Telomerase adds simple sequence repeats to chromosome ends using an internal region of its RNA as a template⁴, and is required for the indefinite proliferation of primary human cells⁵. We find that primary fibroblasts and lymphoblasts from DKC-affected males are not detectably deficient in conventional H/ACA small nucleolar RNA accumulation or function; however, DKC cells have a lower level of telomerase RNA, produce lower levels of telomerase activity and have shorter telomeres than matched normal cells. The pathology of DKC is consistent with compromised telomerase function leading to a defect in telomere maintenance, which may limit the proliferative capacity of human somatic cells in epithelia and blood.