title: Comparison of codon usage measures and their applicability in prediction of microbial gene expressivity.
abstract: BACKGROUND
  There are a number of methods (also called: measures) currently in use that quantify codon usage in genes. These measures are often influenced by other sequence properties, such as length. This can introduce strong methodological bias into measurements; therefore we attempted to develop a method free from such dependencies. One of the common applications of codon usage analyses is to quantitatively predict gene expressivity.
  
  
  RESULTS
  We compared the performance of several commonly used measures and a novel method we introduce in this paper--Measure Independent of Length and Composition (MILC). Large, randomly generated sequence sets were used to test for dependence on (i) sequence length, (ii) overall amount of codon bias and (iii) codon bias discrepancy in the sequences. A derivative of the method, named MELP (MILC-based Expression Level Predictor) can be used to quantitatively predict gene expression levels from genomic data. It was compared to other similar predictors by examining their correlation with actual, experimentally obtained mRNA or protein abundances.
  
  
  CONCLUSIONS
  We have established that MILC is a generally applicable measure, being resistant to changes in gene length and overall nucleotide composition, and introducing little noise into measurements. Other methods, however, may also be appropriate in certain applications. Our efforts to quantitatively predict gene expression levels in several prokaryotes and unicellular eukaryotes met with varying levels of success, depending on the experimental dataset and predictor used. Out of all methods, MELP and Rainer Merkl's GCB method had the most consistent behaviour. A 'reference set' containing known ribosomal protein genes appears to be a valid starting point for a codon usage-based expressivity prediction.
authors: Division of Biology, Department of Molecular Biology, Faculty of Science, Zagreb University, Rooseveltov trg 6, 10000 Zagreb, Croatia. fsupek@public.srce.hr
authors: Fran
authors: F
authors: Supek
authors: Kristian
authors: K
authors: Vlahovicek
mesh_terms: D016009:Chi-Square Distribution; D003062:Codon / Q000032:analysis*; D019295:Computational Biology / Q000379:methods*; D015964:Gene Expression Regulation, Bacterial
chemical_list: D003062:Codon