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Fig. 9. Subhierarchy levels of the spliceosomal assembly network. Red highlighted transitions depict exemplarily T-invariant
13, which describes one possible scenario of E-complex assembly as shown in Fig. 8. (Colours are visible in the online version
of the article at
www.iospress.nl
.)
et al.
, 2000; F orch
et al.
, 2002]. Consequently, these T-invariants can be differentiated into three
groups:
(a) T-invariants i15, i16 (i66, i67) describe the E-complex formation via U1 contacts to the branch
point bound splicing factor SF1 (
t58.U1 SF1 bdg
) and the joining of the auxiliary factor U2AF,
after its recognition of the polypyrimidine tract
t59.U1 SF1 U2AF bdg
. Dependent on the U2
maturation via SF3b125, there exist again two different T-invariants for this mode of E-complex
formation.
(b) The presence of the splicing factor SC35, has been found to facilitate 5'ss recognition
(
t17.U170K U2AF35 bdg
), but required the U1-complex and U2AF [MacMillan
et al.
, 1997].
Hereby, the protein FBP11 helps to bridge U1 and SF1, a constellation, which is in agreement
with the observation that SF1 and U2AF bind cooperatively to the branch point and polypyrim-
