University of Cologne
The sequences deleted from the Ac derivatives are within the 5' untranscribed region of Ac (pKU19), the untranslated region of the Ac transcript (pKU33) or within the long open reading frame of the Ac sequence (pKU4). By Southern analysis the structural integrity of the Ac derivatives and the flanking T-DNA was confirmed. All Ac derivatives tested so far were integrated in the plant genome at their original position in the T-DNA.
Northern hybridisation with short Ac homologous probes was performed on ten independently transformed tobacco plants that had been selected for resistance to hygromycin. From previous experiments with kanamycin-resistant plants it is known that the intact Ac is transcribed after excision from the T-DNA in form of the 3.5kb mRNA also found in maize.
All Ac derivatives still integrated in the T-DNA are transcribed
in a complex manner. In every case more than one Ac-homologous transcript
spanning the whole transcription unit of Ac could be detected on
the Northern blots. In some cases the autonomous Ac transcript starting
at the Ac promoter and terminating at the polyadenylation signal
near the 3' end of Ac could be detected (pKU19, pKU33), but most
of the Ac homologous RNAs are readthrough transcripts of various
sizes (2.0kb - 13kb) initiated outside of Ac, as was shown by hybridisation
with a single stranded probe from the normally untranscribed 5' end of
Ac. It is unclear whether readthrough transcripts starting at the
1' promoter or farther upstream on the T-DNA are able to produce the Ac
transposase if the long open reading frame is intact and the element is
inserted in sense orientation with respect to the 1' promoter sequence
like in pKU19 or pKU33. B. Baker et al. showed that frequency of excision
of the intact Ac is independent of the element's orientation. In
this case readthrough transcription of Ac is not necessary for excision
from the T-DNA.
to the MNL 63 On-Line Index
Return to the Maize Newsletter Index
Return to the Maize Genome Database Page