Martin McGuinness said the party did not have any knowledge of any alleged contact with witnesses
A Sinn Féin politician has resigned from the Northern Ireland Assembly.
It follows political controversy over allegations regarding a witness during a Stormont committee hearing.
In a statement, Sinn Féin Chief Whip Carál Ní Chuilín said: "Daithí McKay has resigned as MLA for North Antrim with immediate effect and has been suspended from Sinn Féin.
"His letter of resignation has been submitted to the Speaker's office," she added.
The allegations are based what are reported to be a series of leaked messages between Mr McKay, Mr Bryson and another Twitter user believed to be a Sinn Féin member.
Earlier, Sinn Féin's Martin McGuinness said the party did not have any knowledge of any alleged contact with witnesses appearing before the inquiry.
Mr McGuinness said: "If the allegations of inappropriate contact prove to be true, then Daithí McKay needs to seriously consider his position as an MLA.
"I want to state categorically that I had absolutely no knowledge of this exchange or contact. And having spoken to all relevant personnel in the Assembly I am now entirely satisfied that Sinn Féin had no knowledge of any such contact," he added.
The committee was established to investigate the alleged irregularities around the sale of the Project Eagle loans worth around €1.4bn.
Mr Bryson alleged during the hearing that Peter Robinson was due to benefit from the sale.
Mr Robinson described the allegations as "outrageous and groundless".