To further characterize both the typical ascidian SNBP PI and the Styela P2 component, a more detailed study of the SNBPs from Styela plicata was performed.
This could account for one of the modes of rapid protein evolution required for the K-to-R changes involved in the H1-to-PL-to-P-type transition that has repeatedly occurred in the course of SNBP evolution.
There is no doubt that the phenomenon described here is not the only mechanism involved in the transition from lysine to arginine during the SNBP type transition.
Sperm nuclear basic proteins (SNBPs) are the chromosomal proteins that are found associated with DNA in sperm nuclei at the end of spermiogenesis.
The compositional heterogeneity and potential structural variability of SNBPs were first envisaged from the early comparative studies of the SNBPs from marine molluscs in what has become a seminal paper on this topic (Subirana et al., 1973).
The structural characterization of the SNBPs of the surf clam Spissula solidissima, one of the species studied in Subirana et al.
Table 1 Sperm nuclear basic proteins (SNBPs) cited in this paper: R/K ratio and representative species References: (1) Strickland et al., 1976; (2) Lewis et al., 2004b; (3) Lewis et al.
By the end of the 1980s, the SNBPs of several echinoderms and many vertebrate species had been characterized.
The first tunicate SNBPs characterized were from the stalked ascidian Styela montereyensis (Chiva et al., 1990).