A new analytical method has been used to examine the set of 40 exon/intron boundaries within the rat embryonic myosin heavy chain (MHCemb) gene. It has also been applied to an additional set of 850 splice sequences selected from GenBank. Strong evidence is obtained for the involvement of 3' ends but not 5' ends of exon sequences in splice site recognition. It can be determined that signal sequences of 5' intron ends concentrate near the splice borders, while the distributions of the 3' intron ends have a diffuse character. The possibility of re-interpreting some known features, in terms of the absence of certain elements rather than the presence of elements forming sequence determinants, is discussed. The analysis undertaken enabled us to work out a more detailed set of recognition sequence requirements for the splicing of nuclear pre-mRNA. In addition to requirements which have already been established we suggest the following: the 'AG-absence' in the immediate 3' terminal intron sequences; and a minimal match between a particular sequence and the known exon/intron consensus sequence of 5' splice junctions.

An algorithm has been developed for the identification of unknown patterns which are distinctive for a set of short DNA sequences believed to be functionally equivalent. A pattern is defined as being a string, containing fully or partially specified nucleotides at each position of the string. The advantage of this 'vague' definition of the pattern is that it imposes minimum constraints on the characterization of patterns. A new feature of the approach developed here is that it allows a 'fair' simultaneous testing of patterns of all degrees of degeneracy. This analysis is based on an evaluation of inhomogeneity in the empirical occurrence distribution of any such pattern within a set of sequences. The use of the nonparametric kernel density estimation of Parzen allows one to assess small disturbances among the sequence alignments. The method also makes it possible to identify sequence subsets with different characteristic patterns. This algorithm was implemented in the analysis of patterns characteristic of sets of promoters, terminators and splice junction sequences. The results are compared with those obtained by other methods.