Dinoflagellates are biflagellated unicellular eukaryotes widely spread all over the aquatic world and well-known for their harmful blooms. They are characterized by their chromosomes always condensed during the cell cycle and by an unusual mitosis called dinomitosis which shows an extranuclear spindle crossing the permanent nuclear envelope via cytoplasmic channels. One of their prominent features which is unique among the eukaryotes is the absence of histones and nucleosomal organization. This raises the problem of condensation of a high quantity of their genomic DNA as well as the replication and transcription mechanisms. Dinoflagellates could use some divergent alternative mechanisms for these prosesses probably involving new proteins. We already described a nuclear protein Dinap1 (Dinoflagellate nuclear associated protein 1) expressed only in G1 phase, in the species Crypthecodinium cohnii. The presence of two WW domains led to the hypothesis that Dinap1 could form a multiprotein complex involved in the transcription regulation. WW domains are known as protein-protein interaction modules which recognize a proline-rich sequence. We used the protein-protein recognition property of the WW domains to screen a cDNA library of C. cohnii and find Dinap1 ligands. Five differents clones called Dip for Dinap1 interacting protein have been isolated. The Dip1 protein contains a PPTY motif, able to bind to the Dinap1 WW domains, and displays two new WW domains. To address the question of the Dinap1-Dip1 complex function, a new screen was performed to identify Dip1 ligands. This led us to the isolation of three new proteins, Dap B, Dap C and Dap G for Dip1 associated protein. The interactions between all these proteins as well as their abilities to bind DNA and their action in an in vitro transcription assay have been investigated.