¹Institute of Biological Sciences, Faculty of Science, ²Department of Chemistry,
Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia

Received I December 1999 / Accepted 17 April 2000

Abstract.
In Escherichia coli, the arginine repressor protein C terminal domain of ArgR (ArgRc) regulates the transcription of L arginine biosynthetic genes and is involved in Xer site specific recombination. ArgR requires L arginine, its co repressor, for DNA binding and hexamerization. X ray crystallographic data of the hexameric ArgRc in the presence of L arginine has been reported by Van Duyne et al in 1996. This paper presents the results from the molecular modeling studies of the ArgRc L arginine interactions. Hydrogen atoms were added to the molecular data of ArgRc protein obtained from the Brookhaven Protein Databank at 2.2 angstrom (A) resolution. The molecule was minimized using the Discover module of the MSI Insight 11 software to ensure that all the hydrogen atoms are in the appropriate position. The computer model has revealed additional information on the protein ligand interaction not mentioned in the published X ray analysis. Amongst the interesting information obtained are models of the interactions between two L arginine molecules interfacing in a "circular fashion" within four subunits of ArgRc. It was also observed that the L arginine ArgRc interactions extends from the centre of the hexamer to the surface area that are joined to the hinge region of the N terminal domain.

Keywords: Molecular modeling, arginine repressor protein, L arginine, Escherichia coli K 12

¹Department of Bioscience and Biotechnology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia,
43600, Bangi, Selangor ²Malaysian Palm Oil Board, P.O. Box 10620, 50720 Kuala Lumpur, Malaysia

Received 19 September 1999 / Accepted 25 February 2000

Abstract.
Oil palm Elaeis guineensis Jacq is the second largest contributor of edible oil to the total fat and oil production in the world. Malaysia is at present the largest producer and exporter of palm oil. Breeding programs are being carried out in order to increase the yield, quality of oil as well as other agronomically important characters. Understanding the genetic diversity in germplasm materials is of prime importance in these breeding programmes. In this study we employed the method of AFLP to study the genetic variation present in an oil palm germplasm collection. We screened germplasm collected from Nigeria, Madagascar, Democratic Republic of Congo (Congo) and Gambia. Ten palms from each country were selected. All together 38 genotypes were analyzed by the AFLP technique using three primer combinations of EcoRl and Mse l. The total number of bands scored was 233 of which 206 (88%) were polymorphic. The total number of bands produced by different primer pair combinations ranged from 64 to 101. Analyses of the results were carried out to determine the degree of heterogeneity and similarity between the population and two dendrograms were generated.

Keywords: Oil palm, AFLP, germplasm, polymorphism, Elaeis guineensis

R&D Centre for Biotechnology LIPI, Jl. Raya Bogor Km 46 Cibinong 16911, P.O.Box 422 Bogor, Indonesia

Received IO December 1999 / Accepled 1 June 2000

Abstract.
An attempt to increase maturation and regeneration of embryoids derived from anther culture of Pometia pinnata was conducted by applying different composition of medium, desiccation and incubation conditions to different ranges of size of embryoids. The effects of glutamine alone (I mg/1) or in combination with ABA (2 mg/1) added to half strength WP medium, or ABA alone added to full strength WP medium containing 0.01 mg/1 NAA and I mg/1 kinetin on three ranges of embryoid sizes i.e. 1 3mm, 3 5 mm, 5 8 mm were compared. Some embryoids or clumps of embryogenic callus were dessicated, by culturing them on a Whatman filter paper placed on semi solid half strength WP medium. Some embryoids were incubated in the dark and compared to those incubated under light. Various factors affecting the storage and germination of encapsulated embryos as artificial seeds, were also investigated. Results showed that all the factors assessed played critical roles in the maturation and regeneration of embryoids. The ability of 60% encapsulated embryoids to germinate after storage of up to 20 days in empty petri dishes enabled them to be treated as seeds.

Keywords: Embryonic callus, embryoids, anther culture, artificial seeds, regeneration

1. Ismail* and S.M. Smith

Institute of Cell and Molecular Biology, University of Edinburgh, the King's Buildings, Mayfield Road, Edinburgh, EH9 3JH, United Kingdom

Received 16 June 2000 / Accepted 28 July 2000

Abstract.
Regulation of malate synthase (MS) and isocitrate lyase (ICL) gene at the posttranscriptional level was studied using actinomycin D, a transcription inhibitor. Detached roots which contained an abundance of NIS and ICL transcripts due to starvation for 4 days, showed a decrease in mRNA amount of about 50% after 3 h incubation in the presence of 10 ug/mI actinomycin D. In contrast, when sucrose was added together with actinomycin D, MS and ICL mRNA decreased to a much lower level within 3 h. Therefore, NIS and ICL half lives appear much shorter in the presence of sugar. Similar results were obtained with detached cotyledons. Confirmation that actinomycin D had effectively stopped transcription was obtained by showing that it prevented light induced expression of hydroxypyruvate reductase and rubisco genes in cotyledons. Thus, NIS and ICL genes appear to be regulated by sugars at the levels of transcription and mRNA stability.

Keywords: Actinomycin D, cucumber (Cucumis sativus), gene expression, glyoxylate cycle, mRNA stability