Introduction

Abstract

Dynamic, polymorphic, problematic yet intriguing are the general view of the genomic region near the ends of chromosomes. Unlike the generally conserved caps of chromosome ends, the telomeres, for which our understanding of their biology has advanced greatly in recent years, the adjacent telomere-associated sequences (TAS) or subtelomeres remain an enigma. This is in large part due to the technical difficulties in working with repeated sequence regions of the genome both experimentally and in genome projects. The repetitive nature makes it difficult to observe a signal from a specific chromosome end among the noise of all the other ends that look and behave similarly. It also has precluded complete assembly of the regions in genome projects. In virtually all eukaryotes and some prokaryotes, linear chromosomes have dynamic and polymorphic subtelomeric regions. In many cases, a great deal of important biology of the organism is encoded in and regulated by the subtelomeric regions. One generality is that the region tends to encode for genes involved in interacting with the extracellular environment though this is not universal. Recombination, chromatin, gene density, and other properties of the region differ from those of the core of the genome in many organisms, though the specific differences vary between organisms. Perhaps the most well-understood subtelomeres are in the budding yeast Saccharomyces cerevisiae, while the epitome of adaptive use of the properties of the region is found in parasites, such as Plasmodium falciparum and Trypanosoma brucei, causing malaria and sleeping sickness. These parasites utilize the region to escape their hosts’ immune systems through generation of diversity and exquisite control of surface antigen expression. A great deal has been learned from comparison between subtelomeres in different organisms, and the interest in subtelomeres is growing. This book does not cover every aspect of subtelomeres in every organism where they are studied, but provides a broad coverage of the field of subtelomeres in diverse organisms from bacteria to yeast and fungi through plants, insects, parasites, and humans. It should serve as an entry point into the field, hopefully generating an interest in this fascinating region of genomes.