Uttar Pradesh chief secretary Prashant Kumar Misra resigned on Friday.
His resignation was accepted within minutes of its submission, following which Mayawati appointed Atul Gupta.
An officer of the 1974 batch, Gupta was holding the position of the state's industrial development commissioner so far. A number of other top level buraucratic changes were also made simultaneously.
While Misra declined to divulge the reasons behind the unexpected decision, he admitted that it was taken on account of some provocation.
He was to superannuate on August 30 and had no intention of quitting office till Friday morning.
"I took the decision today itself to take voluntary retirement," he told rediff.com.
"I do not wish to discuss the reasons behind it ; all I would like to say is that I have served the state and this country for a good 36 years and have no regrets," he said.
He went on to add, "All In can tell you is that I discussed it with my wife and she fully supported me in this decision."
Differences of opinion with the chief minister had almost led him to put in his papers once earlier when he declined to ratify the clean-chit given to former chief secretary Neera Yadav in a departmental probe by another senior IAS officer.
Neera Yadav had been removed from the top job during the previous Mulayam Singh Yadav regime on grave charges of corruption by the Supreme Court, in a PIL moved against her by a city journalist.
In a related departmental inquiry, Mayawati, however, gave her clean chit after which she took voluntary retirement .
Misra had then objected the manner in which Neera Yadav was absolved of the serious charges of corruption without his concurrence.
He was, however, persuaded by colleagues and friends not to put in his papers then.
What provoked him on Friday to rush his resignation remains unknown.
