When you say "the requirements of similar function", am I right to think you mean that certain genetic sequences must be in place to produce similar functions, and hence the word "requirement"?
If your theory of genetic level convergence was correct then that would presumably be its basis, that a specific genetic sequence was required for a specific trait which has evolved convergently between two disparate species, otherwise you would only have phenotypic/morphological convergence.
Do they believe different genes and sequences can produce similar features and function?
Yes they do. There are some instances, first one to hand might mislead you due to the term 'convergent'.
Convergent Evolution of Amadori Opine Catabolic Systems in Plasmids of Agrobacterium tumefaciensChang-Ho Baek, Stephen K. Farrand, Ko-Eun Lee, Dae-Kyun Park, Jeong Kug Lee, and Kun-Soo Kim1.
Journal of Bacteriology, January 2003, p. 513-524, Vol. 185, No. 2
Deoxyfructosyl glutamine (DFG, referred to elsewhere as dfg) is a naturally occurring Amadori compound found in rotting fruits and vegetables. DFG also is an opine and is found in tumors induced by chrysopine-type strains of Agrobacterium tumefaciens. Such strains catabolize this opine via a pathway coded for by their plasmids. NT1, a derivative of the nopaline-type A. tumefaciens strain C58 lacking pTiC58, can utilize DFG as the sole carbon source. Genes for utilization of DFG were mapped to the 543-kb accessory plasmid pAtC58. Two cosmid clones of pAtC58 allowed UIA5, a plasmid-free derivative of C58, harboring pSa-C that expresses MocC (mannopine [MOP] oxidoreductase that oxidizes MOP to DFG), to grow by using MOP as the sole carbon source. Genetic analysis of subclones indicated that the genes for utilization of DFG are located in a 6.2-kb BglII (Bg2) region adjacent to repABC-type genes probably responsible for the replication of pAtC58. This region contains five open reading frames organized into at least two transcriptional soc (santhopine catabolism) groups: socR and socABCD. Nucleotide sequence analysis and analyses of transposon-insertion mutations in the region showed that SocR negatively regulates the expression of socR itself and socABCD. SocA and SocB are responsible for transport of DFG and MOP. SocA is a homolog of known periplasmic amino acid binding proteins. The N-terminal half of SocB is a homolog of the transmembrane transporter proteins for several amino acids, and the C-terminal half is a homolog of the transporter-associated ATP-binding proteins. SocC and SocD could be responsible for the enzymatic degradation of DFG, being homologs of sugar oxidoreductases and an amadoriase from Corynebacterium sp., respectively. The protein products of socABCD are not related at the amino acid sequence level to those of the moc and mot genes of Ti plasmids responsible for utilization of DFG and MOP, indicating that these two sets of genes and their catabolic pathways have evolved convergently from independent origins.
This paper shows that two distinct groups of genes can be responsible for the catabolism of Amadori opines and that these functionally equivalent genes are not related at the amino acid sequence level.
Or, do they believe there has to be some of the same genes and sequences to produce similar features and function?
Not really although there are some instances where this is arguably the case, not at the genetic level but at the amino acid level. The function of a protein is very tightly coupled to its structure, some interactions will require very specific residue positions indeed. In such a case we might expect to find that a similair protein structure or even 1ary amino acid sequence has evolved convergently, but this need not be reflected in the genetic sequence coding for the protein. So they do not believe that this
has to happen, but it certainly may happen, at the amino acid level at least.
Glutamate Decarboxylase: Computer Studies of Enzyme EvolutionB. S. Sukhareva and O. K. Mamaeva
Biochemistry (Mosc). 2002 Oct;67(10):1180-8
The homology of subunit primary sequence of 40 glutamate decarboxylases (GAD) of different origin was analyzed by multiple alignment. A phylogenetic tree was designed on the basis of the resulting data. The following groups are distinguished in the consensus tree: archeans, bacteria, plant eukaryotes, and animal eukaryotes. The latter are clearly divided into two branches according to two enzyme isoforms. Borders of PLP domains in each enzyme were detected. The consensus phylogenetic tree for PLP domains is structurally rather similar to that obtained for subunits. Twenty homologous motifs of from 15 to 87 amino acid residues were revealed in all GAD studied. The results revealed the division of all of the enzymes into groups with characteristic sets of motifs in each and a fixed order of their arrangement along the sequence. Thus, we can show the divergent evolution of the enzyme. The results of multiple alignments during structural analysis of the 40 GAD confirmed and extended our previous data on conserved residues that arrange the position of the coenzyme (PLP) in the enzyme active center. The following residues should be noted: lysine forming a Schiff base with the PLP aldehyde group, an adjacent histidine, and aspartic acid that establishes a link with nitrogen of the PLP pyridine ring. The homology of the primary sequence fragments was also found in the residues in contact with the PLP phosphate group. Comparison of the GAD amino acid sequence with that of another PLP enzyme, aspartate aminotransferase, revealed a binding site for carboxylic group of the substrate--glutamic acid. The structures carrying out a particular catalytic function of all GAD studied were detected, i.e., convergent evolution of the enzyme was revealed.
In this paper a conserved functional site is identified in a family of functionally related but divergent proteins, actually the case here is a bit iffy, I'm not sure why this couldn't be a case of simply maintaining an ancestral acitve site. More probably this is what is often thought of as parallel evolution, this is distinct from straightforward convergence in that the species being compared are thought to have evolved the same functional solutions in similar ways due to having similar initial systems to act as a substrate.
Convergent evolution of disease resistance gene specificity in two flowering plant families.Ashfield T, Ong LE, Nobuta K, Schneider CM, Innes RW.
Plant Cell. 2004 Feb;16(2):309-18. Epub 2004 Jan 23.
Plant disease resistance (R) genes that mediate recognition of the same pathogen determinant sometimes can be found in distantly related plant families. This observation implies that some R gene alleles may have been conserved throughout the diversification of land plants. To address this question, we have compared R genes from Glycine max (soybean), Rpg1-b, and Arabidopsis thaliana, RPM1, that mediate recognition of the same type III effector protein from Pseudomonas syringae, AvrB. RPM1 has been cloned previously, and here, we describe the isolation of Rpg1-b. Although RPM1 and Rpg1-b both belong to the coiled-coil nucleotide binding site (NBS) Leu-rich repeat (LRR) class of R genes, they share only limited sequence similarity outside the conserved domains characteristic of this class. Phylogenetic analyses of A. thaliana and legume NBS-LRR sequences demonstrate that Rpg1-b and RPM1 are not orthologous. We conclude that convergent evolution, rather than the conservation of an ancient specificity, is responsible for the generation of these AvrB-specific genes.
Where disease resitance genes from 2 divergent lineages are shown to have developed a number of amino acid sequence similarities in concert with having similar targets.
TTFN,
WK
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