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The SIR2 (silent information regulator 2) gene family has diverse functions in yeast including gene silencing, DNA repair, cell-cycle progression, and chromosome fidelity in meiosis and aging. Human homologues, termed sirtuins, are highly conserved but are of unknown function. We previously identified a large imprinted gene domain on 11p15.5 and investigated the 11p15.5 sirtuin SIRT3. Although this gene was not imprinted, we found that it is localized to mitochondria, with a mitochondrial targeting signal within a unique N-terminal peptide sequence. The encoded protein was found also to possess NA[D.sup.+]-dependent histone deacetylase activity. These results suggest a previously unrecognized organelle for sirtuin function and that the role of SIRT3 in mitochondria involves protein deacetylation.

Research has been conducted on the specific cytosolic proteins. The experiments demonstrate that the representatives of the Phox homology domains selectively bind to specific phosphatidylinositol phosphates.

Regulated intramembrane proteolysis (Rip), a control mechanism, is discussed in this review article. The mechanism is conserved from bacteria to humans. Conceptual convergence is now seen in the cell signaling field. Transmembrane proteins can be cleaved within the plane of the membrane of the cell to let out cytosolic fragments. The fragments can go into the nucleus to manage gene transcription. The mechanism is called Rip. Five proteins known or thought to undergo Rip in animal cells are SREBP, APP, Notch, Ire1 and ATF6, and there are two in bacteria.

A model in which MUT-7, guided by transposon-derived dsRNA, represses transposition by degrading transposon-specific messengers and prevents thereby transposase production and transposition, is proposed. It appears that NRAi may work by dsRNA-directed enzymatic RNA degradation. One Tc1 silenced strain of C. elegans has been has been mutagenized. Mutants in which Tc1 was activated in the germline were isolated.

Recent findings relating to lesion-replicating DNA polymerases, of which there are many and which are key participants in translesion replication, are discussed. It appears that yeast, bacteria and humans accomplish tranlesion DNA synthesis by a common mechanism and in each case the main replicase for the organism, unable to bypass the lesion, dissociates from the template to leave a 3' primer terminus before the lesion. Then translesion replication is catalyzed by one of the DNA polymerases recently described.

The second src homology 3 (SH3) region from the NH2 terminus of the Bem1p is important bud formation and suppression of rho3 defect. Boi2p found bound to SH3-2 has a proline-rich region that is critical for displaying Boi2p-Bem1p two-hybrid reaction. THe COOH-terminal is essential for the function of BOI2p in cell growth, while the NH2-terminal is requires for the modulating the function of Bem1p. Rho3p GTPases and Boi proteins function in the maintenance of cell polarity for bud formation.

The 210-kD receptor for egg jelly (REJ) in sea urchin sperm is a modular protein with a similar design to human polycystic kidney disease protein, PKD1. REJ contains one EGF module and two C-type carbohydrate-recognition modules. The 700 residues specific module of the REJ shows the homology. REJ acts as a regulator of sperm-ion channels. It is also involved in the carbohydrate recognition of egg jelly. Tentatively REJ is a type one membrane protein with a 18 residue segment near the COOH terminus.

The endogenous Na+ channel genes from Chinese hamster ovary cells was cloned and purified to examine the properties of inward Na+ channels. Specific polymerase chain reaction fragments from ovarian cells were amplified and analysis of these fragments revealed the presence of intrinsically expressed Na+ channel genes in these cells. These genes displayed considerable homology with similar Na+ channel genes in rats' brain. These data suggested a relative similarity between ovarian and brain-type Na+ channels.

The Hox11 gene family potentially codifies the evolutionary conserved regulatory factors involved with multicellular integration in Porifera and Metazoa. We are now looking for deep homologies at the level of Hox11 gene regulation. One kilobase upstream of the transcription initiation site of human Hox11, mouse Hox11 and Porifera Hox11 (EmH-3, Ephydatia muelleri, and prox2, Ephydatia fiuviatilis) were aligned (Clustal). We found six putative elements (Transfactor) present in the same position in all the sequences (AP, IK2, CAAT, USF-Q6 LMO2COM, and CEBPB). To test whether these elements play conserved functions among Porifera and Mammalia, seven fragments with different 5' upstream regions of the Emil-3 promoter, ranging from -173 to -538, were fused to the reporter gene Luciferase (Promega); their activity was tested in cell extracts of transiently transfected mammalian cell lineages. The K562, but not 3T3 and HL-60, lineages express endogenous Hox11. The functional test on promoters wase also performed on differentiated K562 (sodium-butyrate) and HL-60 (retinoic acid). The profile of activity of the Emil-3 promoter was independent of the endogenous expression of Hox11 gene, but dependent of the differentiation stage of the cell lineage. The activation of the fragment 7231 (containing the IK element) and the inhibition capacity of the fragment -279 (containing the USF element) were more pronounced in less differentiated cell lineages, indicating a downregulation of IK and USF in differentiated cells. These results also suggest the presence of positive regulatory regions close to the transcription start site of the Hox11 gene (IK and CAAT). (Supported by FAPERJ/FUJB.)

We describe the unique development and branching of lobed thalli in Hydrobryum japonicum. Lobe formation begins with meristem initiation at random sites near the thallus margin fringed by protective tissues. As the protective tissues are successively peeled off particularly in the growing new lobes, the lobes become naked and then become fringed again by new protective tissues that develop from the marginal part of the new meristems. Subsequently the meristems become less active and are differentiated into parenchymatous ground tissue at maturity. The random pattern of meristem formation during the sporadic development gives rise to a nonorderly branching pattern of the thalli. Some other lobes (~10%) are regenerated from injured parts of the thalli. The vegetative shoots arise endogenously near the thallus margin and are enclosed by the nonvascular strand nets. The rudimentary shoot apices remain embedded in the thalli. The thalli, though remarkably different from typical roots of other angiosperms, might be extremely transformed roots. Key words: developmental morphology; homology; Hydrobryum japonicum; meristem; Podostemaceae; root; root cap; shoot.