Among the 21 genes, 16 could be categorized in the Gene Ontology (GO) of biological process and 15 in molecular function (results not shown).
Biological processes (level 4) are dominated by macromolecule metabolism, including again cyclic compound processing, somehow confirming the Molecular function results ('Response to stress' ranks fifth in Level 3 Biological processes, with about 4% of the hits, which is compatible with results in [610]).
Additionally, the classification of the gene products based on their molecular function resulted in 8 different categories (Figure 4C), among which the binding function represents the largest group (90.5%).
The largely predominant molecular functions resulted to be binding (GO 0005488) and catalytic activity (GO 0003824).
From BLASTx results, a majority of molecular function ontology results (≥1000 contigs) were for binding, especially protein and nucleic acid binding, and for hydrolase, catalytic, transferase, oxidoreductase, structural molecule, and ion transporter activity (Figure 3A).
In this case again, the match between phenotypic trait and gene presence is usually imperfect, primarily because of gene displacements and functional takeovers, or, in other words, relatively frequent functional convergence of genes at the molecular level, when different species use proteins with unrelated sequence and structure to perform a molecular function that results in the same phenotype.
The relatively small number of terms added to the molecular function class results from the combination of the small number of tagged instances (less than 200) and a highly restricted class that includes a restricted set of types of binding and activity classes.
In addition, Molecular Function GO results were tallied across all 4 treatment categories and are summarized in Table 4.
The mapping of gene ontology functional annotation terms onto the non-redundant full length sequences resulted in 901 of our feline cDNA sequences becoming associated with 647 unique gene ontology molecular function annotation terms resulting in 3219 annotation-gene relationships.
A key challenge in phenotypic screens is that disrupting genes, even when they have close molecular functions, can result in characteristically different organism-level phenotypes.
However, many non-homologous proteins share molecular function as a result of convergent evolution, [91] and variations can produce enzymes with similar function but differing sequence motifs [92].
