Although the protein localisation data depends solely on expression of exogenous Buc-GFP, it is highly likely that the endogenous protein behaves in a similar fashion, although it is not certain when the endogenous protein is actually expressed. While Buc RNA disappears from germ plasm in later oogenesis, it persists in a dispersed state at nearly constant levels through oogenesis and into embryonic development, so it is likely that Buc protein is a constituent of mature zebrafish germ plasm. The Xenopus homologue of Bucky ball is Xvelo1. Its RNA is excluded from the mitochondrial cloud in pre-vitellogenic oocytes and in late oogenesis it is localised to the vegetal cortex. As a result this was characterised as late pathway, Vg1-like, localisation. It is expressed as two splice variants. The longer transcript, which we call XveloFL, encodes an 88 kDa protein with no conserved protein motifs which would provide insight into its biological function. There is a shorter splice variant that introduces a frame shift in the C-terminal region, and this RNA has the same temporal expression pattern as the larger transcript. There are Xvelo1/Buc homologues throughout vertebrates, although those in eutherian mammals are more diverged; in humans the RNA lacks a complete open Gambogic-acid reading frame, suggesting that it has lost its function altogether, or functions as an RNA without translation. Since eutherian mammals lack germ plasm, this fits with a primary role for Buc in germ plasm organisation. An interesting feature of the Xenopus Xvelo1 locus is that it overlaps the polycomb1 locus, being transcribed in the opposite direction into the extremely long 39UTR of XPc1. We have recently reported that fluorescently tagged Hermes protein, like injected fluorescent germ plasm RNAs, is localised into the germ plasm RNPs of vitellogenic oocytes and eggs. Since Hermes is absent from late pathway particles we felt that the identification of Hermes binding partners would shed further light on the special properties of germ plasm. Consequently we have screened for partners of Hermes using the yeast two-hybrid system. This has allowed the identification of several candidate proteins, which include the two Xvelo1 homologues of Bucky ball, and two RNA binding proteins, Rbm24b and Rbm42b. We show that the two protein products of the Xvelo1 gene are naturally present in Xenopus germ plasm, in association with Hermes. We also provide evidence that the two Rbm proteins are candidate germ 
plasm constituents, because they locate sufficiently closely to Hermes in RNP particles to interact in bimolecular fluorescence complementation assays. In addition, depletion of one of them alters germ plasm morphology. The single RRM-containing protein Hermes is present in the RNP particles of mature Xenopus oocyte germ plasm, as well as in their precursors in the earlier mitochondrial cloud. Although it is present elsewhere in the oocyte, including the nucleus, it is absent from late pathway particles of the vegetal cortex. Thus we argued that identifying Hermes binding partners would help us to understand the special nature of germ plasm RNA storage units. Here we Dexrazoxane hydrochloride report a number of candidate proteins that interact with Hermes and provide evidence, in some cases, that these interactions actually occur in germ plasm, or in other instances that they could do so if the proteins are naturally expressed in oocytes. The fact that these interactions occur in yeast, in the presence only of fragments of the encoding mRNAs, shows that the protein interactions detected are independent of specific interactions with oocyte RNAs.