Delete many-to-many entity in Entity Framework

I have a database for University journal and trying to make an application to work with it using Entity Framework, WPF and MVVM. It contains tables:

• University_Subject (Subject_ID (PK), SubjectName)

• University_Teacher (Teacher_ID (PK), other fields with info)

• University_TeacherSubject (Teacher_ID (FK), Subject_ID(FK)) - for many-to-many connection upper tables

• University_Group (Group_ID (PK), other info)

• Universiti_GroupSubject (Group_ID (FK), Subject_ID (FK)) - for connection Groups and Subjects
• University_Schedule (Lesson_ID (PK), Group_ID (FK), Teacher_ID(FK), Subject_ID(FK), ) - uses IDs from other tables.

Main trouble I've faced with: how to correctly delete Subject Entity? I need to delete subject without connected entities (Teacher have to stay, it can have other subjects; Group also has other subjects)

In SQL deletion looks like:

-Delete row in TeacherSubject table;

-delete row in GroupSubject table;

-delete row in Schedule talbe;

-delete Subject;

But in Entity Framework I don't have TeacherSubject,GroupSubject tables -> they are presented as navigation properties.

Code I've tried to use but there is an exception (An unhandled exception of type 'System.Data.Entity.Infrastructure.DbUpdateException' occurred in EntityFramework.dll Additional information: Unable to update the EntitySet 'University_TeaSubj' because it has a DefiningQuery and no element exists in the element to support the current operation.):

void DeleteSubjectFromDB(object parameter)
    {
        using (_ujc = new UJContext())
        {
            var tmp = _ujc.University_Subject.Where(s => s.Subject_ID == SelectedSubject.Subject_ID).FirstOrDefault();

            if (tmp!=null)
            {
                //Delete Lessons with SubjectID from schedule
                var lessonlst = _ujc.University_Schedule
                    .Where(l => l.Subject_ID == tmp.Subject_ID).AsEnumerable();
                foreach (var ls in lessonlst)
                {
                    _ujc.University_Schedule.Remove(ls);
                }

                foreach (var teach in _ujc.University_Teacher)
                {
                    if (teach.University_Subject.Contains(tmp))
                        teach.University_Subject.Remove(tmp);
                }
                tmp.University_Teacher.Clear();

                tmp.University_Group.Clear();
                foreach (var gr in _ujc.University_Group)
                {
                    if (gr.University_Subject.Contains(tmp))
                        gr.University_Subject.Remove(tmp);
                }

                _ujc.Entry<University_Subject>(tmp).State = 
                    System.Data.Entity.EntityState.Deleted;

                _ujc.SaveChanges();
                SelectedSubject = null;
                UpdateSubjects();
            }
        }
    }

Sorry, I can't attach DB and EF diagram, because of reputation.

Thank you in advance for the help.