What's the difference between the "present perfect" and the "present perfect subjunctive"??

LS 3

....Transcriptional Repair

yah, so it says that RNA polymerase scans for lesions. Does that mean that transcription actually provides another proofreading mechanism?

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Deutsch Eins

So...I don't get what the difference between nominative and accusative possessive adjectives is...and they're almost the same in spelling.