Pdr5p is the yeast Saccharomyces cerevisiae ATPbinding cassette transporter conferring resistance to several unrelated drugs. Its high overproduction in Pdr1p transcription factor mutants allows us to study the molecular mechanism of multidrug transport and substrate specificity. We have developed new in vivo and in vitro assays of Pdr5p-mediated drug transport. We show that in spite of little sequence homology, and inverted topology in respect to that of mammalian P-glycoproteins, Pdr5p shares with them common substrates. Pdr5p extrudes rhodamines 6G and 123, from intact yeast cells in an energy-dependent manner. Plasma membrane preparations from a Pdr5p-overproducing strain exhibit ATP hydrolysis-dependent, osmotically sensitive rhodamine 6G fluorescence quenching. The quenching is competitively inhibited by micromolar concentrations of many anticancer drugs, such as vinblastine, vincristine, taxol, and verapamil, and of ionophoric peptides as well as steroids. In contrast, other anticancer drugs, like colchicine and some multidrug resistance modifiers, such as quinidine, exert noncompetitive inhibition. Our experimental system opens new possibilities for the analysis of structure-function relationship of multidrug transporter substrates and inhibitors.

lenides 2 in 50-XOViO yields a s yellow oils. Selected spectroscopic data for 2f: 'HNMR(300MHz.CDCIJ:ii = 0.82(t.J=7.0Hz.bHj.1 65(dq.J=7.0,7.0 Hz, 4Hj. 2.2X Is, 2H). 4.76 (t. J =7.0 Hz. 2 H). 7.19 (dd. J = 7 5, 7.5 Hz, 2H). 7.33 (dd..~=~. S ,~. S H Z ,~H ) .~.~S (~. J =~.~H~.~H ) .~.~S (~. J =~S H~.~H ) :~~C N M R (75 MH7. CDCI,): 6 =10.3, 31.3. 74.7. 126.4, 128.3. 129.1. 130.0. 135.3. 146.5: "Se N M R (76 MHz, CDCI,): d = 456.1: [1]:" = + 262.0 ( c = I , CHCI,,): correct elemental analysis foi-C,,H,,0,Se2.Addition ofthe diselenides 2 to atyrene: 2 (0.1 nimol) was placed in dry diethyl ether (4 inL) under argon 'it -78°C and bromine (0.1 1 minol. 0.1 1 mL of a 1 M solutioii in CCI,) wis added. After 10 min silver triflate (72 mg. 0.28 minol) in methanol (0.1 mL) was added atid the mixture was stirred for 20 min at -78 ~ C. The reaction solution s a s cooled to -100 C and treated with styrene (0.4 mmol, 0.046 mL). After the mixture had been stirred Tor 2 h. .~~r~i.-colIidine (0.3 mniol, 0.04 inL) was added. ;ind the resultant mixture was heated to 20 C and washed with 7 % aqueous citric acid solution ( 5 mL). The organic phase was dried with MgSO,. and after remowl of the solwnt under vacuum. thc addition product 3 was purilied by column chroinatosraphy on silica (pentnne: rrrr-butylmethyl ether 3 : I ) . Selected apectroscopic data for 3f. 'H NMR (300 MHz. CDCI,): 6 = 0.98 (t. J =7.4 HL. 3H). 1.79 (quin,J =7.4H7. 2H). 2.41 (s. IH). 3.10-3 30(m. 2H). 3.24(s. 3Hj.4.36 (dd. J = 8 5. 5 HL. I H ) , 5.04 (in. 1Hj. 7.13-7.51 (m. 9H); "C NMR (75 MHz. 139.7. 133.7, 140 8. 140 0: correct elemental analysis Ibr C',,H,,O,Se.

Today's miniature devices and biological systems share the fact that their dynamics and properties cannot be understood in terms of macroscopic concepts, but require a thorough understanding of the nanoscale structuring. This structuring is often very heterogeneous, both in time and in space, and is difficult or impossible to resolve with traditional approaches. In this Progress Report, we will discuss how single‐molecule microscopy—and defocused wide‐field imaging in particular—can be used to shed light on these phenomena.

The importance of the modular structure 'fluor-spacer-amine' is pointed out for the design of fluorescent molecular sensors for p H according to the principle of photoinduced electron transfer (PET). Anthracen-9-yl methylamines (24) and some azacrown ether analogues (1 5 and 23) are examined in this context. They show p H -dependent fluorescence quantum yields describable by eqn. ( 5) while all other electronic spectral parameters remain essentially pH-invariant. The range of pK, values of these sensors are understandable in terms of macrocyclic effects and the transmission of electric fields across the anthracene short axis. Phase-shift fluorometric determination of the fluorescence lifetimes of these sensors allows the calculation of the rate constant of PET in their proton-free form t o be 1 Ole-1 0" s-', with the diamines 23 and 24b exhibiting the faster rates.

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