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Fig. 1. Alignment of the Dd-STATa, b and c sequences after removal of their simple
sequence component. The Accession Number of the complete predicted sequence of
Dd-STATb is AJ581661 but here a truncated form of the sequence is presented.
The N-terminal halves of Dd-STATa, b and c contain tracts of glutamine,
asparagines and threonine. These are encoded by CAA repeats, a feature common
to many Dictyostelium genes. In this alignment, Q, N and T tracts
equal to or longer than three residues were omitted, to give Dd-STATa'
(633 of 707 residues), Dd-STATb' (978 of 1147 residues)and
Dd-STATc' (819 of 929 residues). The three STATs display only scattered
regions of short homology in their N-terminal-proximal regions. No functions
have thus far been mapped to the N-terminal-proximal regions of Dd-STATa or
Dd-STATc and a BLAST search using the N-terminal-proximal region of Dd-STATb
also yielded no hits (the search was run at NCBI with amino acids 1 to 505 and
using blastP with an `E' value of 10). The predicted approximate positions of
the DNA binding domains (closely spaced broken line), the SH2 domains (widely
spaced broken line) and the site of the insertion in the Dd-STATb sequence
(broad unbroken line) are indicated by double-headed arrows. The positions of
the arginine to leucine substitution is indicated by a triangle, and the
predicted site of tyrosine phosphorylation is indicated by an asterisk. (B)
Alignment between the SH2 domains of Dd-STATs a to c, human STATs 1 to 6 and
Src. The alignment was generated using ClustalW and then modified by hand to
align the known secondary structure elements from STAT1 and the Src SH2
domain. This alignment was used in modelling the Dd-STATb SH2 domain (STATc).
The dominant inserts are highlighted in yellow; red indicates identical
residues; grey indicates similar residues. The inset shows a phylogenetic tree
generated using the Nearest Neighbour joining method; blue boxes indicate
proteins where a crystal structure is known.
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