Can I submit seuqence data without any published paper, during writing or in press?

Yes you can. It ought to be required at ‘instructions to authors’ of most of journals to submit sequence data to DDBJ (, EMBL-Bank or GanBank) before the paper submission.
During submission of sequence data, select status for your REFERENCE as follows.

• “Unpublished”; In cases of preparing paper, during paper submission, or you do not prepare any publication.
• “In Press”; When your paper is accepted and in press.

Your citations will be appeared at REFERENCE 2 or after on DDBJ flat file.