Highly specific protein sequence motifs for genome analysis - PubMed (original) (raw)

Highly specific protein sequence motifs for genome analysis

C G Nevill-Manning et al. Proc Natl Acad Sci U S A. 1998.

Abstract

We present a method for discovering conserved sequence motifs from families of aligned protein sequences. The method has been implemented as a computer program called EMOTIF (http://motif. stanford.edu/emotif). Given an aligned set of protein sequences, EMOTIF generates a set of motifs with a wide range of specificities and sensitivities. EMOTIF also can generate motifs that describe possible subfamilies of a protein superfamily. A disjunction of such motifs often can represent the entire superfamily with high specificity and sensitivity. We have used EMOTIF to generate sets of motifs from all 7,000 protein alignments in the BLOCKS and PRINTS databases. The resulting database, called IDENTIFY (http://motif. stanford.edu/identify), contains more than 50,000 motifs. For each alignment, the database contains several motifs having a probability of matching a false positive that range from 10(-10) to 10(-5). Highly specific motifs are well suited for searching entire proteomes, while generating very few false predictions. IDENTIFY assigns biological functions to 25-30% of all proteins encoded by the Saccharomyces cerevisiae genome and by several bacterial genomes. In particular, IDENTIFY assigned functions to 172 of proteins of unknown function in the yeast genome.

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Figures

Figure 1

Figure 1

Substitution groups. Groups of amino acids found to occur together in columns of aligned sequences in both the

blocks

and

hssp

databases. Only groups of amino acids that occur together at a significant frequency and are separated from all other amino acids at a level of significance of less than 0.01 are included. The substitution groups are arranged hierarchically to show relationships between their physical properties.

Figure 2

Figure 2

Aligned block of 34 tubulin proteins and two motifs representing these sequences. (a) An aligned block of 34 tubulin proteins and the sequence variation observed among them. (b) One possible sequence motif for the alignment in a that can be formed by using the amino acid substitution groups from Fig. 1. (c) A much more specific sequence motif that can be used to represent the upper 19 tubulin sequences, which form a group more closely related to each other than to the lower 15 sequences.

Figure 3

Figure 3

Enumeration of tubulin motifs by

emotif

.

emotif

generates all possible sequence motifs that can cover at least 30% of 159 tubulin sequences in a training set. Each motif is plotted as a dot in the figure where the horizontal axis gives the coverage of the motif (number of sequences covered in the training set), and the vertical axis plots the specificity of the motif as the probability of matching a random protein segment. The motifs occur in vertical lines because coverage is an integer quantity. The lower curve is the Pareto-optimal curve, which represents the most specific motif at each level of sensitivity.

Figure 4

Figure 4

The number of motifs required to cover at least 90% of the protein family in the

identify

database.

emotif

was used to generate one or more motifs that cover at least 90% of all the sequences in each of 7,000 alignments in the

blocks

or

prints

databases at five different levels of specificity. Plotted are the number of motifs that are required to cover at least 90% of the sequences in the alignment.

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