Tubulin genes of Trypanosoma brucei: a tightly clustered family of alternating genes.

Abstract

African trypanosomes are the causative agents of many medically and economically important diseases of man and domestic animals. The cell body of these blood-dwelling protozoa is enveloped with a dense layer of pellicular microtubules, which confer both motility and mechanical stability on these cells; microtubules are also important components of the flagellum. The major structural components of the microtubuli are two related proteins, a-and fl-tubulin. We have analyzed the genomic organization of a-and f-tubulin genes in Trypanosoma brucei. In this organism, the majority of these genes are arranged in a single, tightly packed cluster of alternating a-and j3-tubulin genes, with a basic repeat length together of 3.6 kilobase pairs. A genomic library of T. brucei was constructed by using the phage vector A 1059, and recombinant phages carrying tubulin genes were isolated by screening the library with heterologous chicken tubulin cDNA probes. The results of restriction endonuclease and hybridization analysis of DNA isolated from recombinant phages, and subcloned fragments thereof, were compatible with the restriction maps derived from digestion and Southern blot hybridization of genomic DNA.Several members of the protozoan genus of Trypanosoma are pathogenic parasites of a wide variety of species, including man. African trypanosomes are the causative agents of human sleeping sickness (1-3) as well as of various economically disastrous diseases of domestic animals (4). Animal trypanosomiasis presently restricts cattle production in infested areas of Africa to less than 15% of the carrying capacity of the land. Thus, the various forms of trypanosomiasis constitute a major obstacle to the economic and social development of much of sub-Saharan Africa.We are currently studying the microtubular system of trypanosomes in view of its potential as a target structure for chemotherapeutic attack. The cell body of trypanosomes is tightly enveloped by a regular array of pellicular microtubules (5), which confer both motility and mechanical stability on these cells. In addition, microtubules are prominently involved in the structure of the flagellum, where they are arranged in the canonical 9 + 2 pattern.The principal components of microtubules are two related but distinct polypeptides, a-and f3-tubulin. Microtubules are formed from these subunits by a reversible polymerization reaction of a/f3-tubulin heterodimers (6). The (8, 9) and tubulin genes (10-14) have confirmed a high degree of evolutionary conservation.All eukaryotic organisms analyzed so far carry more than one copy of both a-and ,-tubulin genes (15-19). The individual genes are unlinked and dispersed throughout the genome (20). In the human genome, several tubulin pseudogenes have been detected in addition to the families of functional tubulin genes (11,12).In this paper, we describe the organization of the tubulin genes in Trypanosoma brucei. In this organism, a-and ,B-tubulin genes are also present in multiple copies but, unlike the situation in most ...

Structure and transcription of the actin gene of Trypanosoma brucei.

“…So far, most housekeeping genes of T. brucei appear to exist in multicopy clusters, such as genes for calmodulin (44), tubulin (38,43), glyceraldehyde phosphate dehydrogenase (20), phosphoglycerate kinase (9), fructose biphosphate aldolase (4), and heat shock protein 70 (10). The only exception reported so far is the gene for triosephosphate isomerase, which is present in only one copy (41).…”

Six Related Nucleoside/Nucleobase Transporters fromTrypanosoma brucei Exhibit Distinct Biochemical Functions

“…Gene multiplicity is a common feature in kinetoplastid protozoa (21), and each gene often encodes the same protein (22). However, in some examples, gene families encode similar but not identical proteins (23,24).…”

Subcellular sequestration of an antigenically unique β‐tubulin

“…Ultrastructural studies reveal several microtubular structures: flagellar axoneme, subpellicular microtubules, and mitotic spindle [Vickerman and Preston, 19761. In the genome of 7: brucei, the tubulin genes are arranged into a single cluster of alternating a-and 6-tubulin genes [Seebeck et al, 1983;Thomashow et al, 19831. The a-and P-tubulin mRNAs differ in size, 1.95 kb and 2.3 kb, respectively; in that each one migrates as a single band [Imboden et al, 19861, there is no evidence for the production of multiple tubulin isotypes.…”