Biology Education

Department of Biology | Lund University

How do cells maintain their chromosomes without telomerase?

Telomeres are specialized structures that define the ends of eukaryotic chromosomes and are essential for keeping their integrity and genome stability. The principal mechanism for maintaining long telomeres is dependent on the enzyme telomerase, which synthesizes the specific repeated sequences at the ends of chromosomes. If telomerase is absent, telomeres will shorten and the cells will die. However, intriguingly, a backup mechanism for alternative telomere maintenance may be activated, known as Alternative Lengthening of Telomeres (ALT). Interestingly, about 10% of cancer cells have aquired ALT for telomere maintenance.

Switching to the ALT pathway occurs at a very low frequency. However, we recently showed that the budding yeast Naumovozyma castellii uses a novel and highly efficient ALT mechanism. N. castellii uses a specific ∼250 bp DNA element for the ALT telomere elongation, which originally resides within the subtelomeric regions, i.e. the regions located internally of the terminal telomeric sequences. Thus, a key for understanding the ALT mechanism resides within the subtelomeric regions.

In this project we will study the genetic requirements of N. castellii ALT cells. To generate mutant yeast strains we will use the CRISPR/Cas9 methodology, which has recently been developed for this species. The mutants will be characterized regarding their survival capacity, growth ability and phenotype, as well as their telomere lengthening mechanism. In this project we will use a variety of molecular biology techniques, such as PCR, DNA preparation, agarose gel electrophoresis, Southern blot hybridization, Sanger sequencing, and microscopy.

Please have look at his reference for a background:
Cohn M., Karademir Andersson, A., Quintilla Mateo R. and Carlsson Möller M. (2019)
Alternative lengthening of telomeres in the budding yeast Naumovozyma castellii.
Genes, Genomes and Genetics (G3), 9: 3345-3358. DOI: 10.1534/g3.119.400428.

Project duration: 45 or 60 credits (MSc)
Preferred starting date: flexible
Required qualifications: Master courses in molecular biology and genetics.

Contact information: Marita Cohn (

A petridish with white lines and dots.                 A microscopic photo of oval grey blobs with small blobs on them.

February 10, 2020

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Molecular Biology