This pathway is very complex and includes many protein components.
In fact, many protein components of extracellular matrix react with each other and with the specific membrane receptors based on their secondary, tertiary, or quaternary structure.
Interesting questions that may be possible to answer by combining single molecule studies and modelling with new experimental systems featuring few to many protein components in different ordered arrangements would be the following.
Key observations include phylogenetic evidence for very ancient origins for many protein import components (Tim21, Tim50, for example) and indications of differences between the outer membrane receptors that recognize the mitochondrial targeting signals, suggesting replacement, rearrangement and/or emergence of new components across the major eukaryotic lineages.
The complexity of the multicomponent phenol monooxygenase is still far from being understood, since many additional protein components have been recently discovered.
Previous studies on DNA replication of Archaea have already shown that the core replication machineries of the eukaryotes and Archaea possess fundamental similarities and have many homologous protein components [ 35], indicative of common ancestry.
Many salivary protein components, such as proline-rich glycoprotein, mucins, immunoglobulins, agglutinin, lactoferrin, cystatins and lysozyme are thought to have a role in defense in the oral cavity [ 31].
TOP1 has been shown to interact with many proteins including components of the holo TFIIIC complex [ 1], TFIID [ 2], p53 [ 3], SV-40 large T antigen [ 4], nucleolin [ 5], the RING finger protein topors [ 6], the RNA splicing factors PSF/p54nrb[ 7] and SF2/ASF [ 8], the cell cycle regulatory protein ARF [ 9], RNA pol II complex [ 10, 11], and HTLV type 1 tax oncoprotein [ 12].
Therefore, given the likely presence of U5, Prp8 and many other spliceosomal protein components as well as a few spliceosomal introns, it seems highly likely that Giardia has a functional major spliceosome containing all five spliceosomal snRNAs.
Such tight mutual dependence requires exquisite co-ordination between the chloroplast, in which the events are happening, and the nucleus, in which many of the protein components are encoded.
This is possibly because of a paucity of convenient and portable assays for monitoring enzyme activity, and of the difficulty of obtaining many of the protein components and complexes in quantities suitable to detailed biophysical characterization.
