Table 3.

Authentic pPORA, accumulating in vivo, does not inhibit either binding or import of transB-DHFR and transPC-DHFR into Pchlide-containing chloroplasts

Precursor	Binding/import, % of added precursor
	transA-DHFR		transB-DHFR		transPC-DHFR
	−5-ALA	+5-ALA	−5-ALA	+5-ALA	−5-ALA	+5-ALA
Binding
CP+pPORA	n.d.	91	93	95	93	94
CP−pPORA	95	93	96	91	93	93
Import
CP+pPORA	n.d.	24	56	58	51	50
CP-pPORA	n.d.	58	55	60	47	52

Chloroplasts bearing the authentic pPORA (CP+pPORA) at their outer envelope were prepared from etiolated barley seedlings that had been exposed to light for 8 h, as described in ref. 38. By analogy, chloroplasts lacking the pPORA (CP-pPORA) were prepared from light-grown plants. Chloroplasts to be used for binding assays were preincubated at 23°C in the dark with 2 mM Mg-ATP plus 5-ALA (+5-ALA) or Mg-ATP plus phosphate buffer instead of 5-ALA (−5-ALA) and repurified, whereas chloroplasts to be used for studying import were supplemented with these compounds just during their incubation with the different radiolabeled precursors. Quantification of binding and import data was done as described in Fig. 1 and Table 2, respectively. n.d., not detectable.