In the Neurospora genome duplicate sequences are detected and altered in the sexual phase. Both copies of duplicate genes are inactivated at high frequency, whether or not they are linked. Restriction sites change, and affected sequences typically become heavily methylated. To characterize the alterations of the DNA, duplicated sequences were isolated before and after one or more sexual cycles. DNA sequencing and heteroduplex analyses demonstrated that the process (termed RIP) produces exclusively G-C to A-T mutations. Changes occur principally at sites where adenine is 3' of the changed cytosine. A sequence duplicated at a distant site in the genome lost approximately 10 percent of its G-C pairs in one passage through a cross. A closely linked duplication of the same sequence that was passed twice through a cross lost about half of its G-C pairs. The results suggest a mechanism for the RIP process.

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BackgroundTrypanosoma brucei subspecies infect humans and animals in sub-Saharan Africa. This early diverging eukaryote shows many novel features in basic biological processes, including the use of polycistronic transcription to generate all protein-coding mRNAs. Therefore we hypothesized that translational control provides a means to tune gene expression during parasite development in mammalian and fly hosts.ResultsWe used ribosome profiling to examine genome-wide protein synthesis in animal-derived slender bloodstream forms and cultured procyclic (insect midgut) forms. About one-third of all CDSs showed statistically significant regulation of protein production between the two stages. Of these, more than two-thirds showed a change in translation efficiency, but few appeared to be controlled by this alone. Ribosomal proteins were translated poorly, especially in animal-derived parasites. A disproportionate number of metabolic enzymes were up-regulated at the mRNA level in procyclic forms, as were variant surface glycoproteins in bloodstream forms. Comparison with cultured bloodstream forms from another strain revealed stage-specific changes in gene expression that transcend strain and growth conditions. Genes with upstream ORFs had lower mean translation efficiency, but no evidence was found for involvement of uORFs in stage-regulation.ConclusionsRibosome profiling revealed that differences in the production of specific proteins in T. brucei bloodstream and procyclic forms are more extensive than predicted by analysis of mRNA abundance. While in vivo and in vitro derived bloodstream forms from different strains are more similar to one another than to procyclic forms, they showed many differences at both the mRNA and protein production level.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-911) contains supplementary material, which is available to authorized users.

BackgroundTrypanosoma brucei, the causative agent of African sleeping sickness, undergoes a complex developmental cycle that takes place in mammalian and insect hosts and is accompanied by changes in metabolism and cellular morphology. While differences in mRNA expression have been described for many genes, genome-wide expression analyses have been largely lacking. Trypanosomatids represent a unique case in eukaryotes in that they transcribe protein-coding genes as large polycistronic units, and rarely regulate gene expression at the level of transcription initiation.ResultsHere we present a comprehensive analysis of mRNA expression in several stages of parasite development. Utilizing microarrays that have multiple copies of multiple probes for each gene, we were able to demonstrate with a high degree of statistical confidence that approximately one-fourth of genes show differences in mRNA expression levels in the stages examined. These include complex patterns of gene expression within gene families, including the large family of variant surface glycoproteins (VSGs) and their relatives, where we have identified a number of constitutively expressed family members. Furthermore, we were able to assess the relative abundance of all transcripts in each stage, identifying the genes that are either weakly or highly expressed. Very few genes show no evidence of expression.ConclusionDespite the lack of gene regulation at the level of transcription initiation, our results reveal extensive regulation of mRNA abundance associated with different life cycle and growth stages. In addition, analysis of variant surface glycoprotein gene expression reveals a more complex picture than previously thought. These data provide a valuable resource to the community of researchers studying this lethal agent.