include SORTING, that sorts, packs and assesses the quality of the experimentally measured diffraction data, and is run in the first step. The program TABLING calculates the continuous Fourier coefficients from the model placed in the artificial cell. The cross-rotation function is carried out by the program ROTING, which uses Crowther's algorithm (Crowther, 1972). TRAING is used to calculate the translation function. Finally FITING is used to refine the orientational and positional parameters of the molecule corresponding to the potential solutions, as a rigid body.

To carry out MR, the AMoRe package can be used. AMoRe constitutes a suite of programs written by Jorge Navaza (Navaza, 1993; Navaza, 1994). These

Conditions for expression of r-bZP3 in SG 13009[pREP4] cells transformed with the pQE-bZP3 plasmid were standardized. Cells were grown till A6oo=0.7 and induced with different concentrations of IPTG (0.5, 1, 2, or 4 mM) for a constant time period (3h) or induced with a 0.5 mM IPTG for different time periods (0, 1, 2, 3 or 5 h). Cells were harvested and analyzed by SDS-PAGE and immunoblot as described above.

containing 2. 2 M formaldehyde and 50 % V /V formamide. The samples were chilled on ice for 5 mins. and loading buffer added. A Taq I digest of phi X 174 DNA, filled-in wi~h Klenow polymerase using 32P-dCTP, was used as size marker for electrophoresis. The gels were run at <5 Vjcm.

Total RNA was resolved in formaldehyde -agarose gels as described by Maniatis et al., ( 1982 ) • In general, the electrophoresis was performed using 1.2 ~ 0 agarose gels containing 2.2 M formaldehyde and 1 X running buffer 0.04 M rnorpholinopropanesulfonic acid -MOPS, pH 7.0; 0.01 M sodium acetate; 0.001 M EDTA ). RNA samples upto 20 ug in 5 ul ) were incubated at 55°c for 15 minutes in 5 X gel buffer

lectrophoresed on 0.7 % -1.2 % agarose gels in TAE or TBE buffer. Choice of the percentage of agarose and the electrophoresis buffer system was made following the guidelines of Maniatis et al., ( 1982 ). In general, upto 1 kb fragments were resolved on 1.2 % agarose gels using TBE buffer. For most other purposes, TAE buffer was used. Agarose gel electrophoresis was carried out as described by Maniatis et al., ( 1982 ) . The run was stopped when the bromophenol blue dye migrated to within 1 em -1.5 em from the edge of ' the gel, except when the sample had fragments smaller than 500 bp, in which case the elctrophoresis was terminated at an earlier stage. The gel was immersed in water containing 0.5 ug I ml ethidium bromide, for 30 minutes, to stain the DNA. When detecting very low amounts of DNA, the staining was done for 60 minutes followed by destaining in 1 mM Mgso4 for one hour at room temperature. The DNA bands were visualised on a short wavelength UV transilluminator ( Fotodyne, Inc., USA and photographed with a Polaroid MP-4 camera using Polaroid type 667 film.

DNA digested with restriction enzymes was

The membranes were suspended (1.4 x 108 cell equivalent) in 250 III of incorporation buffer (50 mM HEPES, pH = 7.4, 25 mM KCI, 5 mM MgCb, 5 mM MnCI2, 0.1 mM TlCK, 1 Ilg/ml leupeptin, 1 mM ATP, 0.5 mM dithiothreitol and 0.4 Ilg/ml tunicamycin). Each assay tube was prepared by adding 12.5 III of 1 % Chaps, 2.8 III of 200 IlM GOP-Man, 10 III of GOP-[3H]-Man (1IlCi) and 25 nmol of synthetic substrate (49). The contents were lyophilized and 250 III of membrane suspension (1 .4 x 108 cell equivalent in incorporation buffer) were added to each tube. The tubes were incubated at 28°C for 20 minutes, cooled to 0 °C and the membranes were pelleted at 4 °C for 10 minutes in a microcentrifuge. The eH] mannosylated products, that were recovered in the supernatant, were mixed with 0.5 ml 100 mM ammonium acetate and applied to a C18 Sep-pak cartridge that had been washed with 5 ml 80% propan-1-01 and 5 ml 100 mM ammonium acetate. The cartridge was washed with 1.5 ml of 100 mM ammonium acetate and then the eluate was reapplied to the same cartridge. The cartridge was subsequently washed with 5 ml of 100 mM ammonium acetate, after which the bound material was eluted with 5 ml of 60% propan-1-01. The final eluate was concentrated and redissolved in 100 III of 60% propan-1-01. One tenth of this volume was taken for scintillation counting. The above assay was then carried out with a range of concentrations of OMJ to assess it's effect on the activity of eMPT enzyme parse.

Typically 400-500ng of DNA was used in each ligation reaction. The ratio of vectorto insert was maintained between 1:3 and 1:5 for cohesive end ligation. The reaction was generally performed in 15μl volume containing ligation buffer (provided by the manufacturer) and 0.075 Weiss unit of T4 DNA ligase at 16ºC overnight (14-16 hours)