Michael Ruf

Structure and expression of the gene coding for the alpha-subunit of DNA-dependent RNA polymerase from the chloroplast genome of Zea mays.

The rpoA gene coding for the alpha-subunit of DNA-dependent RNA polymerase located on the DNA of Zea mays chloroplasts has been characterized with respect to its position on the chloroplast genome and its nucleotide sequence. The amino acid sequence derived for a 39 Kd polypeptide shows strong homology with sequences derived from the rpoA genes of other chloroplast species and with the amino acid sequence of the alpha-subunit from E. coli RNA polymerase. Transcripts of the rpoA gene were identified by Northern hybridization and characterized by S1 mapping using total RNA isolated from maize chloroplasts. Antibodies raised against a synthetic C-terminal heptapeptide show cross reactivity with a 39 Kd polypeptide contained in the stroma fraction of maize chloroplasts. It is concluded that the rpoA gene is a functional gene and that therefore, at least the alpha-subunit of plastidic RNA polymerase, is expressed in chloroplasts.

Occurrence and spacing of ribosome recognition sites in mRNAs of chloroplasts from higher plants

A computer‐aided search for potential ribosome recognition sequences of mRNAs from tobacco chloroplasts shows that more than 90% of mRNA species contain sequences upstream of the respective initiator codons, which allow base pairing with 3′‐terminal sequences of small subunit rRNA. This complementarity in several cases involves 16 S rRNA sequences between the canonical CCUCC sequence and the 3′‐terminal stem/loop structure. The distances between potential ribosome recognition sequences and initiator codons can be up to 25 nucleotides which is much greater when compared to the spacing of 7±2 nucleotides observed for the classical Shine‐Dalgarno sequences in bacterial mRNAs.

MODELLING TRANSITION STATE ANALOGUES AND ENZYME-INHIBITOR COMPLEXES OF ZINC-CONTAINING CLASS II ALDOLASES AND METALLOPROTEASES

Abstract The zinc complex Tp ∗ Znue5f8OH ( 1: Tp ∗ = hydrotris -(3- cumyl ,5- methyl-pyrazolyl)borate ) which is a model of hydrolytic zinc enzymes was reacted with hydroxamic acids and hydroxyketones. Two hydroxamates Tp ∗ Zn-Hya ( 2 : Hya = acetohydroxamate , 3 : Hya = 2-hydroxamato-4-methylpentanoyl-alanyl-glycylamide ) and two ketoalcoholates Tp ∗ Zn-Kea ( 4 : Kea = hydroxyacetonate , 5 : Kea = cumoylacetonate ) were obtained. Crystal structure determinations of 2, 3 and 5 have revealed distorted ZnN 3 O 2 coordinations in each case. The immediate environment of the zinc ion in the hydroxamates closely resembles that in enzyme-(hydroxamate)inhibitor complexes of zinc-containing metalloproteases like collagenases and thermolysin or of class II aldolases like fuculose-1-phoshate aldolase. Like in the enzymes the hydroxamates and the ketoalcoholates can serve as transition state analogues of the enzyme-catalysed reactions.

Pyrazolylborate)zinc Organophosphate Complexes Resulting from Hydrolytic Cleavage of Phosphate Esters

Five different (pyrazolylborate)zinc hydroxide complexes Tp*Zn−OH (1) were used as hydrolytic reagents towards esters of various acids of phosphorus. Trimethyl phosphate and trimethyl phosphite could not be cleaved. Dimethyl and diphenyl phosphite yielded TptBu,MeZn−OPHO(OR) (2, 3). Triphenyl phosphate reacted slowly producing moderate yields of Tp*Zn−OPO(OPh)2 (4). Tris(p-nitrophenyl) phosphate was cleaved rapidly, forming Tp*Zn−OPO(OC6H4NO2)2 (5) and Tp*Zn−OC6H4NO2 (6). Alkylbis(p-nitrophenyl) phosphates showed intermediate reactivity, losing p-nitrophenolate upon hydrolysis and producing Tp*Zn−OPO(OR)(OC6H4NO2) (7, 8). When phosphorus acid diesters were employed, condensation between the Zn−OH and P−OH functions occurred. This proved to be the convenient way of preparing the organophosphate complexes Tp*Zn−OPO(Ph)2 (9), Tp*Zn−OPO(OPh)2 (4), and Tp*Zn−OPO(OC6H4NO2)2 (5). Six structure determinations showed the structural variability of the resulting complexes.

Insertion of CO and SO2 into the N–N bond of [Fe2(CO)6(μ-Ph2N2)]

Abstract The N–N bond of the azobenzene ligand in [Fe 2 (CO) 6 ( μ -Ph 2 N 2 )] ( 1 ) is unusually labile. In addition to being cleaved by incorporation of CO or H 2 , it also inserts CO resulting from phosphine substitution at the iron atoms. Complexes [Fe 2 (CO) 5 (PR 3 )( μ -PhN–CO–NPh)] ( 2a,b ) and [Fe 2 (CO) 4 {P(OMe) 3 } 2 ( μ -PhN–CO–NPh)] ( 2c ) are formed with PPh 3 and P(OMe) 3 . Bis(diphenylphosphino)methane produces [Fe 2 (CO) 4 ( η 1 -dppm) 2 ( μ -PhN–CO–NPh)] ( 2d ). All these complexes also result from [Fe 2 (CO) 6 ( μ -PhN–CO–NPh)] ( 2 ) and the corresponding phosphine. Reaction of 1 with SO 2 yields the insertion product [Fe 2 (CO) 6 ( μ -PhN–SO 2 –NPh)] ( 4 ). Complex 4 does not react with CO at temperatures up to its decomposition point. Its thermal degradation in the absence of CO, however, produces the CO insertion product 2 , which involves SO 2 elimination with intermediate re-formation of 1 . Treatment of 4 with phosphines results only in CO displacement, producing [Fe 2 (CO) 5 P(OMe) 3 ( μ -PhN–SO 2 –NPh)] ( 4b ), [Fe 2 (CO) 4 (PR 3 ) 2 ( μ -PhN–SO 2 –NPh)] ( 4a,c , PR 3 =PPh 3 or P(OMe) 3 ), and [Fe 2 (CO) 4 ( μ -dppm)( μ -PhN–SO 2 –NPh)] ( 4d ). For comparison with the basic structures of 1 , 2 and 4 two CO insertion products and two SO 2 insertion products were characterized by crystal structure determinations.

Reversible insertion of SO2 into the NN bond of [Fe2(CO)6(μ-Ph2N2)]☆

Abstract The unusual lability of the Nue5f8N bond of the azobenzene ligand in [Fe2(CO)6(μ-Ph2N2)] (1) has allowed the insertion of SO2 under normal conditions. The resulting complex [Fe2(CO)6(μ-PhNue5f8SO2ue5f8NPh)] (2) has been shown by structure determination to be a labilized sulphamide derivative. Thermolysis of 2 leads to elimination of SO2 and isolation of [Fe2(CO)6(μ-PhNue5f8COue5f8NPh)] (3), which is also a thermolysis product of 1.

A new pyrazolylborate zinc hydroxide complex capable of cleaving esters, amides and phosphates

The L2·Zn–OH complex of the new ligand L2= hydrotris(3-p-isopropylphenyl-5-methylpyrazolyl)borate is a strong nucleophile which effects cleavage of activated esters, amides, non-activated phosphorus acid esters and diphosphates, thereby providing stoichiometric models of esterase, peptidase and phosphatase enzyme activity.

Insertion of SO2 into the P–P bond of Fe2(CO)6(μ-P2 tBu2)

Abstract The P–P bond in the dinuclear iron complex Fe 2 (CO) 6 (μ-P 2 t Bu 2 ) was found to be labile towards SO 2 insertion, yielding Fe 2 (CO) 6 (μ- t BuP–SO 2 –P t Bu), which was characterized by a structure determination.

Dalton communications. Molecular zinc oxide and sulfide complexes stabilized by pyrazolylborate ligands

The highly encapsulating tris (3-p-cumenyl-5-methylpyrazolyl)borate L and its isomer L′ have been found to create sufficient steric hindrance and electronic saturation to stabilize non-oligomeric Zn–O–Zn and Zn–S–Zn units in the neutral dinuclear complexes [(L′Zn)2O] and [(LZn)2S], the crystal structures of which were determined.